module RBS
  module Unnamed
    # <!-- rdoc-file=hash.c -->
    # `ENV` is a hash-like accessor for environment variables.
    #
    # ### Interaction with the Operating System
    #
    # The `ENV` object interacts with the operating system's environment variables:
    #
    # *   When you get the value for a name in `ENV`, the value is retrieved from
    #     among the current environment variables.
    # *   When you create or set a name-value pair in `ENV`, the name and value are
    #     immediately set in the environment variables.
    # *   When you delete a name-value pair in `ENV`, it is immediately deleted from
    #     the environment variables.
    #
    # ### Names and Values
    #
    # Generally, a name or value is a String.
    #
    # #### Valid Names and Values
    #
    # Each name or value must be one of the following:
    #
    # *   A String.
    # *   An object that responds to #to_str by returning a String, in which case
    #     that String will be used as the name or value.
    #
    # #### Invalid Names and Values
    #
    # A new name:
    #
    # *   May not be the empty string:
    #         ENV[''] = '0'
    #         # Raises Errno::EINVAL (Invalid argument - ruby_setenv())
    #
    # *   May not contain character `"="`:
    #         ENV['='] = '0'
    #         # Raises Errno::EINVAL (Invalid argument - ruby_setenv(=))
    #
    # A new name or value:
    #
    # *   May not be a non-String that does not respond to #to_str:
    #
    #         ENV['foo'] = Object.new
    #         # Raises TypeError (no implicit conversion of Object into String)
    #         ENV[Object.new] = '0'
    #         # Raises TypeError (no implicit conversion of Object into String)
    #
    # *   May not contain the NUL character `"\0"`:
    #
    #         ENV['foo'] = "\0"
    #         # Raises ArgumentError (bad environment variable value: contains null byte)
    #         ENV["\0"] == '0'
    #         # Raises ArgumentError (bad environment variable name: contains null byte)
    #
    # *   May not have an ASCII-incompatible encoding such as UTF-16LE or
    #     ISO-2022-JP:
    #
    #         ENV['foo'] = '0'.force_encoding(Encoding::ISO_2022_JP)
    #         # Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: ISO-2022-JP)
    #         ENV["foo".force_encoding(Encoding::ISO_2022_JP)] = '0'
    #         # Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: ISO-2022-JP)
    #
    # ### About Ordering
    #
    # `ENV` enumerates its name/value pairs in the order found in the operating
    # system's environment variables. Therefore the ordering of `ENV` content is
    # OS-dependent, and may be indeterminate.
    #
    # This will be seen in:
    # *   A Hash returned by an `ENV` method.
    # *   An Enumerator returned by an `ENV` method.
    # *   An Array returned by ENV.keys, ENV.values, or ENV.to_a.
    # *   The String returned by ENV.inspect.
    # *   The Array returned by ENV.shift.
    # *   The name returned by ENV.key.
    #
    # ### About the Examples
    # Some methods in `ENV` return `ENV` itself. Typically, there are many
    # environment variables. It's not useful to display a large `ENV` in the
    # examples here, so most example snippets begin by resetting the contents of
    # `ENV`:
    # *   ENV.replace replaces `ENV` with a new collection of entries.
    # *   ENV.clear empties `ENV`.
    #
    # ### What's Here
    #
    # First, what's elsewhere. Class `ENV`:
    #
    # *   Inherits from [class Object](rdoc-ref:Object@What-27s+Here).
    # *   Extends [module Enumerable](rdoc-ref:Enumerable@What-27s+Here),
    #
    # Here, class `ENV` provides methods that are useful for:
    #
    # *   [Querying](rdoc-ref:ENV@Methods+for+Querying)
    # *   [Assigning](rdoc-ref:ENV@Methods+for+Assigning)
    # *   [Deleting](rdoc-ref:ENV@Methods+for+Deleting)
    # *   [Iterating](rdoc-ref:ENV@Methods+for+Iterating)
    # *   [Converting](rdoc-ref:ENV@Methods+for+Converting)
    # *   [And more ....](rdoc-ref:ENV@More+Methods)
    #
    # #### Methods for Querying
    #
    # *   ::[]: Returns the value for the given environment variable name if it
    #     exists:
    # *   ::empty?: Returns whether `ENV` is empty.
    # *   ::has_value?, ::value?: Returns whether the given value is in `ENV`.
    # *   ::include?, ::has_key?, ::key?, ::member?: Returns whether the given name
    #     is in `ENV`.
    # *   ::key: Returns the name of the first entry with the given value.
    # *   ::size, ::length: Returns the number of entries.
    # *   ::value?: Returns whether any entry has the given value.
    #
    # #### Methods for Assigning
    #
    # *   ::[]=, ::store: Creates, updates, or deletes the named environment
    #     variable.
    # *   ::clear: Removes every environment variable; returns `ENV`:
    # *   ::update, ::merge!: Adds to `ENV` each key/value pair in the given hash.
    # *   ::replace: Replaces the entire content of the `ENV` with the name/value
    #     pairs in the given hash.
    #
    # #### Methods for Deleting
    #
    # *   ::delete: Deletes the named environment variable name if it exists.
    # *   ::delete_if: Deletes entries selected by the block.
    # *   ::keep_if: Deletes entries not selected by the block.
    # *   ::reject!: Similar to #delete_if, but returns `nil` if no change was made.
    # *   ::select!, ::filter!: Deletes entries selected by the block.
    # *   ::shift: Removes and returns the first entry.
    #
    # #### Methods for Iterating
    #
    # *   ::each, ::each_pair: Calls the block with each name/value pair.
    # *   ::each_key: Calls the block with each name.
    # *   ::each_value: Calls the block with each value.
    #
    # #### Methods for Converting
    #
    # *   ::assoc: Returns a 2-element array containing the name and value of the
    #     named environment variable if it exists:
    # *   ::clone: Returns `ENV` (and issues a warning).
    # *   ::except: Returns a hash of all name/value pairs except those given.
    # *   ::fetch: Returns the value for the given name.
    # *   ::inspect: Returns the contents of `ENV` as a string.
    # *   ::invert: Returns a hash whose keys are the `ENV` values, and whose values
    #     are the corresponding `ENV` names.
    # *   ::keys: Returns an array of all names.
    # *   ::rassoc: Returns the name and value of the first found entry that has the
    #     given value.
    # *   ::reject: Returns a hash of those entries not rejected by the block.
    # *   ::select, ::filter: Returns a hash of name/value pairs selected by the
    #     block.
    # *   ::slice: Returns a hash of the given names and their corresponding values.
    # *   ::to_a: Returns the entries as an array of 2-element Arrays.
    # *   ::to_h: Returns a hash of entries selected by the block.
    # *   ::to_hash: Returns a hash of all entries.
    # *   ::to_s: Returns the string `'ENV'`.
    # *   ::values: Returns all values as an array.
    # *   ::values_at: Returns an array of the values for the given name.
    #
    # #### More Methods
    #
    # *   ::dup: Raises an exception.
    # *   ::freeze: Raises an exception.
    # *   ::rehash: Returns `nil`, without modifying `ENV`.
    #
    %a{annotate:rdoc:copy:ENV}
    class ENVClass
      include Enumerable[[ String, String ]]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV[name] -> value
      # -->
      # Returns the value for the environment variable `name` if it exists:
      #     ENV['foo'] = '0'
      #     ENV['foo'] # => "0"
      #
      # Returns `nil` if the named variable does not exist.
      #
      # Raises an exception if `name` is invalid. See [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values).
      #
      %a{annotate:rdoc:copy:ENV.[]}
      def []: (String name) -> String?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.fetch(name)                  -> value
      #   - ENV.fetch(name, default)         -> value
      #   - ENV.fetch(name) { |name| block } -> value
      # -->
      # If `name` is the name of an environment variable, returns its value:
      #     ENV['foo'] = '0'
      #     ENV.fetch('foo') # => '0'
      #
      # Otherwise if a block is given (but not a default value), yields `name` to the
      # block and returns the block's return value:
      #     ENV.fetch('foo') { |name| :need_not_return_a_string } # => :need_not_return_a_string
      #
      # Otherwise if a default value is given (but not a block), returns the default
      # value:
      #     ENV.delete('foo')
      #     ENV.fetch('foo', :default_need_not_be_a_string) # => :default_need_not_be_a_string
      #
      # If the environment variable does not exist and both default and block are
      # given, issues a warning ("warning: block supersedes default value argument"),
      # yields `name` to the block, and returns the block's return value:
      #     ENV.fetch('foo', :default) { |name| :block_return } # => :block_return
      #
      # Raises KeyError if `name` is valid, but not found, and neither default value
      # nor block is given:
      #     ENV.fetch('foo') # Raises KeyError (key not found: "foo")
      #
      # Raises an exception if `name` is invalid. See [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values).
      #
      %a{annotate:rdoc:copy:ENV.fetch}
      def fetch: (String name) -> String
               | [X] (String name, X default) -> (String | X)
               | [X] (String name) { (String) -> X } -> (String | X)

      # <!--
      #   rdoc-file=hash.c
      #   - ENV[name] = value      -> value
      #   - ENV.store(name, value) -> value
      # -->
      # Creates, updates, or deletes the named environment variable, returning the
      # value. Both `name` and `value` may be instances of String. See [Valid Names
      # and Values](rdoc-ref:ENV@Valid+Names+and+Values).
      #
      # *   If the named environment variable does not exist:
      #     *   If `value` is `nil`, does nothing.
      #             ENV.clear
      #             ENV['foo'] = nil # => nil
      #             ENV.include?('foo') # => false
      #             ENV.store('bar', nil) # => nil
      #             ENV.include?('bar') # => false
      #
      #     *   If `value` is not `nil`, creates the environment variable with `name`
      #         and `value`:
      #             # Create 'foo' using ENV.[]=.
      #             ENV['foo'] = '0' # => '0'
      #             ENV['foo'] # => '0'
      #             # Create 'bar' using ENV.store.
      #             ENV.store('bar', '1') # => '1'
      #             ENV['bar'] # => '1'
      #
      # *   If the named environment variable exists:
      #     *   If `value` is not `nil`, updates the environment variable with value
      #         `value`:
      #             # Update 'foo' using ENV.[]=.
      #             ENV['foo'] = '2' # => '2'
      #             ENV['foo'] # => '2'
      #             # Update 'bar' using ENV.store.
      #             ENV.store('bar', '3') # => '3'
      #             ENV['bar'] # => '3'
      #
      #     *   If `value` is `nil`, deletes the environment variable:
      #             # Delete 'foo' using ENV.[]=.
      #             ENV['foo'] = nil # => nil
      #             ENV.include?('foo') # => false
      #             # Delete 'bar' using ENV.store.
      #             ENV.store('bar', nil) # => nil
      #             ENV.include?('bar') # => false
      #
      # Raises an exception if `name` or `value` is invalid. See [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values).
      #
      %a{annotate:rdoc:copy:ENV.[]=}
      def []=: (String name, String? value) -> String?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV[name] = value      -> value
      #   - ENV.store(name, value) -> value
      # -->
      # Creates, updates, or deletes the named environment variable, returning the
      # value. Both `name` and `value` may be instances of String. See [Valid Names
      # and Values](rdoc-ref:ENV@Valid+Names+and+Values).
      #
      # *   If the named environment variable does not exist:
      #     *   If `value` is `nil`, does nothing.
      #             ENV.clear
      #             ENV['foo'] = nil # => nil
      #             ENV.include?('foo') # => false
      #             ENV.store('bar', nil) # => nil
      #             ENV.include?('bar') # => false
      #
      #     *   If `value` is not `nil`, creates the environment variable with `name`
      #         and `value`:
      #             # Create 'foo' using ENV.[]=.
      #             ENV['foo'] = '0' # => '0'
      #             ENV['foo'] # => '0'
      #             # Create 'bar' using ENV.store.
      #             ENV.store('bar', '1') # => '1'
      #             ENV['bar'] # => '1'
      #
      # *   If the named environment variable exists:
      #     *   If `value` is not `nil`, updates the environment variable with value
      #         `value`:
      #             # Update 'foo' using ENV.[]=.
      #             ENV['foo'] = '2' # => '2'
      #             ENV['foo'] # => '2'
      #             # Update 'bar' using ENV.store.
      #             ENV.store('bar', '3') # => '3'
      #             ENV['bar'] # => '3'
      #
      #     *   If `value` is `nil`, deletes the environment variable:
      #             # Delete 'foo' using ENV.[]=.
      #             ENV['foo'] = nil # => nil
      #             ENV.include?('foo') # => false
      #             # Delete 'bar' using ENV.store.
      #             ENV.store('bar', nil) # => nil
      #             ENV.include?('bar') # => false
      #
      # Raises an exception if `name` or `value` is invalid. See [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values).
      #
      %a{annotate:rdoc:copy:ENV.store}
      alias store []=

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.each      { |name, value| block } -> ENV
      #   - ENV.each                              -> an_enumerator
      #   - ENV.each_pair { |name, value| block } -> ENV
      #   - ENV.each_pair                         -> an_enumerator
      # -->
      # Yields each environment variable name and its value as a 2-element Array:
      #     h = {}
      #     ENV.each_pair { |name, value| h[name] = value } # => ENV
      #     h # => {"bar"=>"1", "foo"=>"0"}
      #
      # Returns an Enumerator if no block given:
      #     h = {}
      #     e = ENV.each_pair # => #<Enumerator: {"bar"=>"1", "foo"=>"0"}:each_pair>
      #     e.each { |name, value| h[name] = value } # => ENV
      #     h # => {"bar"=>"1", "foo"=>"0"}
      #
      %a{annotate:rdoc:copy:ENV.each}
      def each: () -> ::Enumerator[[ String, String ], self]
              | () { ([ String, String ]) -> void } -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.each      { |name, value| block } -> ENV
      #   - ENV.each                              -> an_enumerator
      #   - ENV.each_pair { |name, value| block } -> ENV
      #   - ENV.each_pair                         -> an_enumerator
      # -->
      # Yields each environment variable name and its value as a 2-element Array:
      #     h = {}
      #     ENV.each_pair { |name, value| h[name] = value } # => ENV
      #     h # => {"bar"=>"1", "foo"=>"0"}
      #
      # Returns an Enumerator if no block given:
      #     h = {}
      #     e = ENV.each_pair # => #<Enumerator: {"bar"=>"1", "foo"=>"0"}:each_pair>
      #     e.each { |name, value| h[name] = value } # => ENV
      #     h # => {"bar"=>"1", "foo"=>"0"}
      #
      %a{annotate:rdoc:copy:ENV.each_pair}
      def each_pair: () -> ::Enumerator[[ String, String ], self]
                   | () { ([ String, String ]) -> void } -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.each_key { |name| block } -> ENV
      #   - ENV.each_key                  -> an_enumerator
      # -->
      # Yields each environment variable name:
      #     ENV.replace('foo' => '0', 'bar' => '1') # => ENV
      #     names = []
      #     ENV.each_key { |name| names.push(name) } # => ENV
      #     names # => ["bar", "foo"]
      #
      # Returns an Enumerator if no block given:
      #     e = ENV.each_key # => #<Enumerator: {"bar"=>"1", "foo"=>"0"}:each_key>
      #     names = []
      #     e.each { |name| names.push(name) } # => ENV
      #     names # => ["bar", "foo"]
      #
      %a{annotate:rdoc:copy:ENV.each_key}
      def each_key: () -> ::Enumerator[[ String ], self]
                  | () { (String name) -> void } -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.each_value { |value| block } -> ENV
      #   - ENV.each_value                   -> an_enumerator
      # -->
      # Yields each environment variable value:
      #     ENV.replace('foo' => '0', 'bar' => '1') # => ENV
      #     values = []
      #     ENV.each_value { |value| values.push(value) } # => ENV
      #     values # => ["1", "0"]
      #
      # Returns an Enumerator if no block given:
      #     e = ENV.each_value # => #<Enumerator: {"bar"=>"1", "foo"=>"0"}:each_value>
      #     values = []
      #     e.each { |value| values.push(value) } # => ENV
      #     values # => ["1", "0"]
      #
      %a{annotate:rdoc:copy:ENV.each_value}
      def each_value: () -> ::Enumerator[[ String ], self]
                    | () { (String value) -> void } -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.delete(name)                           -> value
      #   - ENV.delete(name) { |name| block }          -> value
      #   - ENV.delete(missing_name)                   -> nil
      #   - ENV.delete(missing_name) { |name| block }  -> block_value
      # -->
      # Deletes the environment variable with `name` if it exists and returns its
      # value:
      #     ENV['foo'] = '0'
      #     ENV.delete('foo') # => '0'
      #
      # If a block is not given and the named environment variable does not exist,
      # returns `nil`.
      #
      # If a block given and the environment variable does not exist, yields `name` to
      # the block and returns the value of the block:
      #     ENV.delete('foo') { |name| name * 2 } # => "foofoo"
      #
      # If a block given and the environment variable exists, deletes the environment
      # variable and returns its value (ignoring the block):
      #     ENV['foo'] = '0'
      #     ENV.delete('foo') { |name| raise 'ignored' } # => "0"
      #
      # Raises an exception if `name` is invalid. See [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values).
      #
      %a{annotate:rdoc:copy:ENV.delete}
      def delete: (String name) -> String?
                | (String name) { (String) -> String } -> String

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.delete_if { |name, value| block } -> ENV
      #   - ENV.delete_if                         -> an_enumerator
      # -->
      # Yields each environment variable name and its value as a 2-element Array,
      # deleting each environment variable for which the block returns a truthy value,
      # and returning ENV (regardless of whether any deletions):
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.delete_if { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"foo"=>"0"}
      #     ENV.delete_if { |name, value| name.start_with?('b') } # => ENV
      #
      # Returns an Enumerator if no block given:
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     e = ENV.delete_if # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:delete_if!>
      #     e.each { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"foo"=>"0"}
      #     e.each { |name, value| name.start_with?('b') } # => ENV
      #
      %a{annotate:rdoc:copy:ENV.delete_if}
      def delete_if: () -> ::Enumerator[[ String, String ], self]
                   | () { (String name, String value) -> boolish } -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.keep_if { |name, value| block } -> ENV
      #   - ENV.keep_if                         -> an_enumerator
      # -->
      # Yields each environment variable name and its value as a 2-element Array,
      # deleting each environment variable for which the block returns `false` or
      # `nil`, and returning ENV:
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.keep_if { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #
      # Returns an Enumerator if no block given:
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     e = ENV.keep_if # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:keep_if>
      #     e.each { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #
      %a{annotate:rdoc:copy:ENV.keep_if}
      def keep_if: () -> ::Enumerator[[ String, String ], self]
                 | () { (String name, String value) -> boolish } -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.slice(*names) -> hash of name/value pairs
      # -->
      # Returns a Hash of the given ENV names and their corresponding values:
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2', 'bat' => '3')
      #     ENV.slice('foo', 'baz') # => {"foo"=>"0", "baz"=>"2"}
      #     ENV.slice('baz', 'foo') # => {"baz"=>"2", "foo"=>"0"}
      #
      # Raises an exception if any of the `names` is invalid (see [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values)):
      #     ENV.slice('foo', 'bar', :bat) # Raises TypeError (no implicit conversion of Symbol into String)
      #
      %a{annotate:rdoc:copy:ENV.slice}
      def slice: (*String names) -> ::Hash[String, String]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.except(*keys) -> a_hash
      # -->
      # Returns a hash except the given keys from ENV and their values.
      #
      #     ENV                       #=> {"LANG"=>"en_US.UTF-8", "TERM"=>"xterm-256color", "HOME"=>"/Users/rhc"}
      #     ENV.except("TERM","HOME") #=> {"LANG"=>"en_US.UTF-8"}
      #
      %a{annotate:rdoc:copy:ENV.except}
      def except: (*String names) -> ::Hash[String, String]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.clear -> ENV
      # -->
      # Removes every environment variable; returns ENV:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.size # => 2
      #     ENV.clear # => ENV
      #     ENV.size # => 0
      #
      %a{annotate:rdoc:copy:ENV.clear}
      def clear: () -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.reject { |name, value| block } -> hash of name/value pairs
      #   - ENV.reject                         -> an_enumerator
      # -->
      # Yields each environment variable name and its value as a 2-element Array.
      # Returns a Hash whose items are determined by the block. When the block returns
      # a truthy value, the name/value pair is added to the return Hash; otherwise the
      # pair is ignored:
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.reject { |name, value| name.start_with?('b') } # => {"foo"=>"0"}
      #
      # Returns an Enumerator if no block given:
      #     e = ENV.reject
      #     e.each { |name, value| name.start_with?('b') } # => {"foo"=>"0"}
      #
      %a{annotate:rdoc:copy:ENV.reject}
      def reject: () -> ::Enumerator[[ String, String ], self]
                | () { (String name, String value) -> boolish } -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.reject! { |name, value| block } -> ENV or nil
      #   - ENV.reject!                         -> an_enumerator
      # -->
      # Similar to ENV.delete_if, but returns `nil` if no changes were made.
      #
      # Yields each environment variable name and its value as a 2-element Array,
      # deleting each environment variable for which the block returns a truthy value,
      # and returning ENV (if any deletions) or `nil` (if not):
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.reject! { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"foo"=>"0"}
      #     ENV.reject! { |name, value| name.start_with?('b') } # => nil
      #
      # Returns an Enumerator if no block given:
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     e = ENV.reject! # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:reject!>
      #     e.each { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"foo"=>"0"}
      #     e.each { |name, value| name.start_with?('b') } # => nil
      #
      %a{annotate:rdoc:copy:ENV.reject!}
      def reject!: () -> ::Enumerator[[ String, String ], self?]
                 | () { (String name, String value) -> boolish } -> self?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.select { |name, value| block } -> hash of name/value pairs
      #   - ENV.select                         -> an_enumerator
      #   - ENV.filter { |name, value| block } -> hash of name/value pairs
      #   - ENV.filter                         -> an_enumerator
      # -->
      # Yields each environment variable name and its value as a 2-element Array,
      # returning a Hash of the names and values for which the block returns a truthy
      # value:
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.select { |name, value| name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
      #     ENV.filter { |name, value| name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
      #
      # Returns an Enumerator if no block given:
      #     e = ENV.select # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:select>
      #     e.each { |name, value | name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
      #     e = ENV.filter # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:filter>
      #     e.each { |name, value | name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
      #
      %a{annotate:rdoc:copy:ENV.select}
      def select: () -> ::Enumerator[[ String, String ], ::Hash[String, String]]
                | () { (String name, String value) -> boolish } -> ::Hash[String, String]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.select { |name, value| block } -> hash of name/value pairs
      #   - ENV.select                         -> an_enumerator
      #   - ENV.filter { |name, value| block } -> hash of name/value pairs
      #   - ENV.filter                         -> an_enumerator
      # -->
      # Yields each environment variable name and its value as a 2-element Array,
      # returning a Hash of the names and values for which the block returns a truthy
      # value:
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.select { |name, value| name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
      #     ENV.filter { |name, value| name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
      #
      # Returns an Enumerator if no block given:
      #     e = ENV.select # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:select>
      #     e.each { |name, value | name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
      #     e = ENV.filter # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:filter>
      #     e.each { |name, value | name.start_with?('b') } # => {"bar"=>"1", "baz"=>"2"}
      #
      %a{annotate:rdoc:copy:ENV.filter}
      alias filter select

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.select! { |name, value| block } -> ENV or nil
      #   - ENV.select!                         -> an_enumerator
      #   - ENV.filter! { |name, value| block } -> ENV or nil
      #   - ENV.filter!                         -> an_enumerator
      # -->
      # Yields each environment variable name and its value as a 2-element Array,
      # deleting each entry for which the block returns `false` or `nil`, and
      # returning ENV if any deletions made, or `nil` otherwise:
      #
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.select! { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #     ENV.select! { |name, value| true } # => nil
      #
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.filter! { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #     ENV.filter! { |name, value| true } # => nil
      #
      # Returns an Enumerator if no block given:
      #
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     e = ENV.select! # => #<Enumerator: {"bar"=>"1", "baz"=>"2"}:select!>
      #     e.each { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #     e.each { |name, value| true } # => nil
      #
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     e = ENV.filter! # => #<Enumerator: {"bar"=>"1", "baz"=>"2"}:filter!>
      #     e.each { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #     e.each { |name, value| true } # => nil
      #
      %a{annotate:rdoc:copy:ENV.select!}
      def select!: () -> ::Enumerator[[ String, String ], self?]
                 | () { (String name, String value) -> boolish } -> self?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.select! { |name, value| block } -> ENV or nil
      #   - ENV.select!                         -> an_enumerator
      #   - ENV.filter! { |name, value| block } -> ENV or nil
      #   - ENV.filter!                         -> an_enumerator
      # -->
      # Yields each environment variable name and its value as a 2-element Array,
      # deleting each entry for which the block returns `false` or `nil`, and
      # returning ENV if any deletions made, or `nil` otherwise:
      #
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.select! { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #     ENV.select! { |name, value| true } # => nil
      #
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.filter! { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #     ENV.filter! { |name, value| true } # => nil
      #
      # Returns an Enumerator if no block given:
      #
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     e = ENV.select! # => #<Enumerator: {"bar"=>"1", "baz"=>"2"}:select!>
      #     e.each { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #     e.each { |name, value| true } # => nil
      #
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     e = ENV.filter! # => #<Enumerator: {"bar"=>"1", "baz"=>"2"}:filter!>
      #     e.each { |name, value| name.start_with?('b') } # => ENV
      #     ENV # => {"bar"=>"1", "baz"=>"2"}
      #     e.each { |name, value| true } # => nil
      #
      %a{annotate:rdoc:copy:ENV.filter!}
      alias filter! select!

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.shift -> [name, value] or nil
      # -->
      # Removes the first environment variable from ENV and returns a 2-element Array
      # containing its name and value:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.to_hash # => {'bar' => '1', 'foo' => '0'}
      #     ENV.shift # => ['bar', '1']
      #     ENV.to_hash # => {'foo' => '0'}
      #
      # Exactly which environment variable is "first" is OS-dependent. See [About
      # Ordering](rdoc-ref:ENV@About+Ordering).
      #
      # Returns `nil` if the environment is empty.
      #
      %a{annotate:rdoc:copy:ENV.shift}
      def shift: () -> [ String, String ]?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.invert -> hash of value/name pairs
      # -->
      # Returns a Hash whose keys are the ENV values, and whose values are the
      # corresponding ENV names:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.invert # => {"1"=>"bar", "0"=>"foo"}
      #
      # For a duplicate ENV value, overwrites the hash entry:
      #     ENV.replace('foo' => '0', 'bar' => '0')
      #     ENV.invert # => {"0"=>"foo"}
      #
      # Note that the order of the ENV processing is OS-dependent, which means that
      # the order of overwriting is also OS-dependent. See [About
      # Ordering](rdoc-ref:ENV@About+Ordering).
      #
      %a{annotate:rdoc:copy:ENV.invert}
      def invert: () -> ::Hash[String, String]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.replace(hash) -> ENV
      # -->
      # Replaces the entire content of the environment variables with the name/value
      # pairs in the given `hash`; returns ENV.
      #
      # Replaces the content of ENV with the given pairs:
      #     ENV.replace('foo' => '0', 'bar' => '1') # => ENV
      #     ENV.to_hash # => {"bar"=>"1", "foo"=>"0"}
      #
      # Raises an exception if a name or value is invalid (see [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values)):
      #     ENV.replace('foo' => '0', :bar => '1') # Raises TypeError (no implicit conversion of Symbol into String)
      #     ENV.replace('foo' => '0', 'bar' => 1) # Raises TypeError (no implicit conversion of Integer into String)
      #     ENV.to_hash # => {"bar"=>"1", "foo"=>"0"}
      #
      %a{annotate:rdoc:copy:ENV.replace}
      def replace: (Hash[String, String]) -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.update                                              -> ENV
      #   - ENV.update(*hashes)                                     -> ENV
      #   - ENV.update(*hashes) { |name, env_val, hash_val| block } -> ENV
      #   - ENV.merge!                                              -> ENV
      #   - ENV.merge!(*hashes)                                     -> ENV
      #   - ENV.merge!(*hashes) { |name, env_val, hash_val| block } -> ENV
      # -->
      # Adds to ENV each key/value pair in the given `hash`; returns ENV:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.merge!('baz' => '2', 'bat' => '3') # => {"bar"=>"1", "bat"=>"3", "baz"=>"2", "foo"=>"0"}
      #
      # Deletes the ENV entry for a hash value that is `nil`:
      #     ENV.merge!('baz' => nil, 'bat' => nil) # => {"bar"=>"1", "foo"=>"0"}
      #
      # For an already-existing name, if no block given, overwrites the ENV value:
      #     ENV.merge!('foo' => '4') # => {"bar"=>"1", "foo"=>"4"}
      #
      # For an already-existing name, if block given, yields the name, its ENV value,
      # and its hash value; the block's return value becomes the new name:
      #     ENV.merge!('foo' => '5') { |name, env_val, hash_val | env_val + hash_val } # => {"bar"=>"1", "foo"=>"45"}
      #
      # Raises an exception if a name or value is invalid (see [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values));
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.merge!('foo' => '6', :bar => '7', 'baz' => '9') # Raises TypeError (no implicit conversion of Symbol into String)
      #     ENV # => {"bar"=>"1", "foo"=>"6"}
      #     ENV.merge!('foo' => '7', 'bar' => 8, 'baz' => '9') # Raises TypeError (no implicit conversion of Integer into String)
      #     ENV # => {"bar"=>"1", "foo"=>"7"}
      #
      # Raises an exception if the block returns an invalid name: (see [Invalid Names
      # and Values](rdoc-ref:ENV@Invalid+Names+and+Values)):
      #     ENV.merge!('bat' => '8', 'foo' => '9') { |name, env_val, hash_val | 10 } # Raises TypeError (no implicit conversion of Integer into String)
      #     ENV # => {"bar"=>"1", "bat"=>"8", "foo"=>"7"}
      #
      # Note that for the exceptions above, hash pairs preceding an invalid name or
      # value are processed normally; those following are ignored.
      #
      %a{annotate:rdoc:copy:ENV.update}
      def update: (Hash[String, String?]) -> self
                | (Hash[String, String?]) { (String name, String env_val, String? hash_val) -> String } -> self

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.update                                              -> ENV
      #   - ENV.update(*hashes)                                     -> ENV
      #   - ENV.update(*hashes) { |name, env_val, hash_val| block } -> ENV
      #   - ENV.merge!                                              -> ENV
      #   - ENV.merge!(*hashes)                                     -> ENV
      #   - ENV.merge!(*hashes) { |name, env_val, hash_val| block } -> ENV
      # -->
      # Adds to ENV each key/value pair in the given `hash`; returns ENV:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.merge!('baz' => '2', 'bat' => '3') # => {"bar"=>"1", "bat"=>"3", "baz"=>"2", "foo"=>"0"}
      #
      # Deletes the ENV entry for a hash value that is `nil`:
      #     ENV.merge!('baz' => nil, 'bat' => nil) # => {"bar"=>"1", "foo"=>"0"}
      #
      # For an already-existing name, if no block given, overwrites the ENV value:
      #     ENV.merge!('foo' => '4') # => {"bar"=>"1", "foo"=>"4"}
      #
      # For an already-existing name, if block given, yields the name, its ENV value,
      # and its hash value; the block's return value becomes the new name:
      #     ENV.merge!('foo' => '5') { |name, env_val, hash_val | env_val + hash_val } # => {"bar"=>"1", "foo"=>"45"}
      #
      # Raises an exception if a name or value is invalid (see [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values));
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.merge!('foo' => '6', :bar => '7', 'baz' => '9') # Raises TypeError (no implicit conversion of Symbol into String)
      #     ENV # => {"bar"=>"1", "foo"=>"6"}
      #     ENV.merge!('foo' => '7', 'bar' => 8, 'baz' => '9') # Raises TypeError (no implicit conversion of Integer into String)
      #     ENV # => {"bar"=>"1", "foo"=>"7"}
      #
      # Raises an exception if the block returns an invalid name: (see [Invalid Names
      # and Values](rdoc-ref:ENV@Invalid+Names+and+Values)):
      #     ENV.merge!('bat' => '8', 'foo' => '9') { |name, env_val, hash_val | 10 } # Raises TypeError (no implicit conversion of Integer into String)
      #     ENV # => {"bar"=>"1", "bat"=>"8", "foo"=>"7"}
      #
      # Note that for the exceptions above, hash pairs preceding an invalid name or
      # value are processed normally; those following are ignored.
      #
      %a{annotate:rdoc:copy:ENV.merge!}
      alias merge! update

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.rehash -> nil
      # -->
      # (Provided for compatibility with Hash.)
      #
      # Does not modify ENV; returns `nil`.
      #
      %a{annotate:rdoc:copy:ENV.rehash}
      def rehash: () -> nil

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.to_a -> array of 2-element arrays
      # -->
      # Returns the contents of ENV as an Array of 2-element Arrays, each of which is
      # a name/value pair:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.to_a # => [["bar", "1"], ["foo", "0"]]
      #
      %a{annotate:rdoc:copy:ENV.to_a}
      def to_a: () -> ::Array[[ String, String ]]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.to_s -> "ENV"
      # -->
      # Returns String 'ENV':
      #     ENV.to_s # => "ENV"
      #
      %a{annotate:rdoc:copy:ENV.to_s}
      def to_s: () -> "ENV"

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.key(value) -> name or nil
      # -->
      # Returns the name of the first environment variable with `value`, if it exists:
      #     ENV.replace('foo' => '0', 'bar' => '0')
      #     ENV.key('0') # => "foo"
      #
      # The order in which environment variables are examined is OS-dependent. See
      # [About Ordering](rdoc-ref:ENV@About+Ordering).
      #
      # Returns `nil` if there is no such value.
      #
      # Raises an exception if `value` is invalid:
      #     ENV.key(Object.new) # raises TypeError (no implicit conversion of Object into String)
      #
      # See [Invalid Names and Values](rdoc-ref:ENV@Invalid+Names+and+Values).
      #
      %a{annotate:rdoc:copy:ENV.key}
      def key: (String value) -> String?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.length -> an_integer
      #   - ENV.size   -> an_integer
      # -->
      # Returns the count of environment variables:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.length # => 2
      #     ENV.size # => 2
      #
      %a{annotate:rdoc:copy:ENV.size}
      def size: () -> Integer

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.length -> an_integer
      #   - ENV.size   -> an_integer
      # -->
      # Returns the count of environment variables:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.length # => 2
      #     ENV.size # => 2
      #
      %a{annotate:rdoc:copy:ENV.length}
      alias length size

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.empty? -> true or false
      # -->
      # Returns `true` when there are no environment variables, `false` otherwise:
      #     ENV.clear
      #     ENV.empty? # => true
      #     ENV['foo'] = '0'
      #     ENV.empty? # => false
      #
      %a{annotate:rdoc:copy:ENV.empty?}
      def empty?: () -> bool

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.keys -> array of names
      # -->
      # Returns all variable names in an Array:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.keys # => ['bar', 'foo']
      #
      # The order of the names is OS-dependent. See [About
      # Ordering](rdoc-ref:ENV@About+Ordering).
      #
      # Returns the empty Array if ENV is empty.
      #
      %a{annotate:rdoc:copy:ENV.keys}
      def keys: () -> ::Array[String]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.values -> array of values
      # -->
      # Returns all environment variable values in an Array:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.values # => ['1', '0']
      #
      # The order of the values is OS-dependent. See [About
      # Ordering](rdoc-ref:ENV@About+Ordering).
      #
      # Returns the empty Array if ENV is empty.
      #
      %a{annotate:rdoc:copy:ENV.values}
      def values: () -> ::Array[String]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.values_at(*names) -> array of values
      # -->
      # Returns an Array containing the environment variable values associated with
      # the given names:
      #     ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
      #     ENV.values_at('foo', 'baz') # => ["0", "2"]
      #
      # Returns `nil` in the Array for each name that is not an ENV name:
      #     ENV.values_at('foo', 'bat', 'bar', 'bam') # => ["0", nil, "1", nil]
      #
      # Returns an empty Array if no names given.
      #
      # Raises an exception if any name is invalid. See [Invalid Names and
      # Values](rdoc-ref:ENV@Invalid+Names+and+Values).
      #
      %a{annotate:rdoc:copy:ENV.values_at}
      def values_at: (*String names) -> ::Array[String?]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.include?(name) -> true or false
      #   - ENV.has_key?(name) -> true or false
      #   - ENV.member?(name)  -> true or false
      #   - ENV.key?(name)     -> true or false
      # -->
      # Returns `true` if there is an environment variable with the given `name`:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.include?('foo') # => true
      #
      # Returns `false` if `name` is a valid String and there is no such environment
      # variable:
      #     ENV.include?('baz') # => false
      #
      # Returns `false` if `name` is the empty String or is a String containing
      # character `'='`:
      #     ENV.include?('') # => false
      #     ENV.include?('=') # => false
      #
      # Raises an exception if `name` is a String containing the NUL character `"\0"`:
      #     ENV.include?("\0") # Raises ArgumentError (bad environment variable name: contains null byte)
      #
      # Raises an exception if `name` has an encoding that is not ASCII-compatible:
      #     ENV.include?("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
      #     # Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)
      #
      # Raises an exception if `name` is not a String:
      #     ENV.include?(Object.new) # TypeError (no implicit conversion of Object into String)
      #
      %a{annotate:rdoc:copy:ENV.include?}
      def include?: (String name) -> bool

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.include?(name) -> true or false
      #   - ENV.has_key?(name) -> true or false
      #   - ENV.member?(name)  -> true or false
      #   - ENV.key?(name)     -> true or false
      # -->
      # Returns `true` if there is an environment variable with the given `name`:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.include?('foo') # => true
      #
      # Returns `false` if `name` is a valid String and there is no such environment
      # variable:
      #     ENV.include?('baz') # => false
      #
      # Returns `false` if `name` is the empty String or is a String containing
      # character `'='`:
      #     ENV.include?('') # => false
      #     ENV.include?('=') # => false
      #
      # Raises an exception if `name` is a String containing the NUL character `"\0"`:
      #     ENV.include?("\0") # Raises ArgumentError (bad environment variable name: contains null byte)
      #
      # Raises an exception if `name` has an encoding that is not ASCII-compatible:
      #     ENV.include?("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
      #     # Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)
      #
      # Raises an exception if `name` is not a String:
      #     ENV.include?(Object.new) # TypeError (no implicit conversion of Object into String)
      #
      %a{annotate:rdoc:copy:ENV.member?}
      alias member? include?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.include?(name) -> true or false
      #   - ENV.has_key?(name) -> true or false
      #   - ENV.member?(name)  -> true or false
      #   - ENV.key?(name)     -> true or false
      # -->
      # Returns `true` if there is an environment variable with the given `name`:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.include?('foo') # => true
      #
      # Returns `false` if `name` is a valid String and there is no such environment
      # variable:
      #     ENV.include?('baz') # => false
      #
      # Returns `false` if `name` is the empty String or is a String containing
      # character `'='`:
      #     ENV.include?('') # => false
      #     ENV.include?('=') # => false
      #
      # Raises an exception if `name` is a String containing the NUL character `"\0"`:
      #     ENV.include?("\0") # Raises ArgumentError (bad environment variable name: contains null byte)
      #
      # Raises an exception if `name` has an encoding that is not ASCII-compatible:
      #     ENV.include?("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
      #     # Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)
      #
      # Raises an exception if `name` is not a String:
      #     ENV.include?(Object.new) # TypeError (no implicit conversion of Object into String)
      #
      %a{annotate:rdoc:copy:ENV.has_key?}
      alias has_key? include?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.value?(value)     -> true or false
      #   - ENV.has_value?(value) -> true or false
      # -->
      # Returns `true` if `value` is the value for some environment variable name,
      # `false` otherwise:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.value?('0') # => true
      #     ENV.has_value?('0') # => true
      #     ENV.value?('2') # => false
      #     ENV.has_value?('2') # => false
      #
      %a{annotate:rdoc:copy:ENV.has_value?}
      def has_value?: (String value) -> bool

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.value?(value)     -> true or false
      #   - ENV.has_value?(value) -> true or false
      # -->
      # Returns `true` if `value` is the value for some environment variable name,
      # `false` otherwise:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.value?('0') # => true
      #     ENV.has_value?('0') # => true
      #     ENV.value?('2') # => false
      #     ENV.has_value?('2') # => false
      #
      %a{annotate:rdoc:copy:ENV.value?}
      alias value? has_value?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.include?(name) -> true or false
      #   - ENV.has_key?(name) -> true or false
      #   - ENV.member?(name)  -> true or false
      #   - ENV.key?(name)     -> true or false
      # -->
      # Returns `true` if there is an environment variable with the given `name`:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.include?('foo') # => true
      #
      # Returns `false` if `name` is a valid String and there is no such environment
      # variable:
      #     ENV.include?('baz') # => false
      #
      # Returns `false` if `name` is the empty String or is a String containing
      # character `'='`:
      #     ENV.include?('') # => false
      #     ENV.include?('=') # => false
      #
      # Raises an exception if `name` is a String containing the NUL character `"\0"`:
      #     ENV.include?("\0") # Raises ArgumentError (bad environment variable name: contains null byte)
      #
      # Raises an exception if `name` has an encoding that is not ASCII-compatible:
      #     ENV.include?("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
      #     # Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)
      #
      # Raises an exception if `name` is not a String:
      #     ENV.include?(Object.new) # TypeError (no implicit conversion of Object into String)
      #
      %a{annotate:rdoc:copy:ENV.key?}
      alias key? include?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.to_hash -> hash of name/value pairs
      # -->
      # Returns a Hash containing all name/value pairs from ENV:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.to_hash # => {"bar"=>"1", "foo"=>"0"}
      #
      %a{annotate:rdoc:copy:ENV.to_hash}
      def to_hash: () -> ::Hash[String, String]

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.assoc(name) -> [name, value] or nil
      # -->
      # Returns a 2-element Array containing the name and value of the environment
      # variable for `name` if it exists:
      #     ENV.replace('foo' => '0', 'bar' => '1')
      #     ENV.assoc('foo') # => ['foo', '0']
      #
      # Returns `nil` if `name` is a valid String and there is no such environment
      # variable.
      #
      # Returns `nil` if `name` is the empty String or is a String containing
      # character `'='`.
      #
      # Raises an exception if `name` is a String containing the NUL character `"\0"`:
      #     ENV.assoc("\0") # Raises ArgumentError (bad environment variable name: contains null byte)
      #
      # Raises an exception if `name` has an encoding that is not ASCII-compatible:
      #     ENV.assoc("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
      #     # Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)
      #
      # Raises an exception if `name` is not a String:
      #     ENV.assoc(Object.new) # TypeError (no implicit conversion of Object into String)
      #
      %a{annotate:rdoc:copy:ENV.assoc}
      def assoc: (String name) -> [ String, String ]?

      # <!--
      #   rdoc-file=hash.c
      #   - ENV.rassoc(value) -> [name, value] or nil
      # -->
      # Returns a 2-element Array containing the name and value of the **first**
      # **found** environment variable that has value `value`, if one exists:
      #     ENV.replace('foo' => '0', 'bar' => '0')
      #     ENV.rassoc('0') # => ["bar", "0"]
      #
      # The order in which environment variables are examined is OS-dependent. See
      # [About Ordering](rdoc-ref:ENV@About+Ordering).
      #
      # Returns `nil` if there is no such environment variable.
      #
      %a{annotate:rdoc:copy:ENV.rassoc}
      def rassoc: (String value) -> [ String, String ]?
    end
  end
end
