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    // implements the unary operator "op &T"
    // based on "op T" where T is expected to be `Copy`able
    macro_rules! forward_ref_unop {
        (impl $imp:ident, $method:ident for $t:ty) => {
            forward_ref_unop!(impl $imp, $method for $t,
                    #[stable(feature = "rust1", since = "1.0.0")]);
        };
        (impl $imp:ident, $method:ident for $t:ty, #[$attr:meta]) => {
            #[$attr]
            impl $imp for &$t {
                type Output = <$t as $imp>::Output;

                #[inline]
                fn $method(self) -> <$t as $imp>::Output {
                    $imp::$method(*self)
                }
            }
        }
    }

    // implements binary operators "&T op U", "T op &U", "&T op &U"
    // based on "T op U" where T and U are expected to be `Copy`able
    macro_rules! forward_ref_binop {
        (impl $imp:ident, $method:ident for $t:ty, $u:ty) => {
            forward_ref_binop!(impl $imp, $method for $t, $u,
                    #[stable(feature = "rust1", since = "1.0.0")]);
        };
        (impl $imp:ident, $method:ident for $t:ty, $u:ty, #[$attr:meta]) => {
            #[$attr]
            impl<'a> $imp<$u> for &'a $t {
                type Output = <$t as $imp<$u>>::Output;

                #[inline]
                fn $method(self, other: $u) -> <$t as $imp<$u>>::Output {
                    $imp::$method(*self, other)
                }
            }

            #[$attr]
            impl $imp<&$u> for $t {
                type Output = <$t as $imp<$u>>::Output;

                #[inline]
                fn $method(self, other: &$u) -> <$t as $imp<$u>>::Output {
                    $imp::$method(self, *other)
                }
            }

            #[$attr]
            impl $imp<&$u> for &$t {
                type Output = <$t as $imp<$u>>::Output;

                #[inline]
                fn $method(self, other: &$u) -> <$t as $imp<$u>>::Output {
                    $imp::$method(*self, *other)
                }
            }
        }
    }

    // implements "T op= &U", based on "T op= U"
    // where U is expected to be `Copy`able
    macro_rules! forward_ref_op_assign {
        (impl $imp:ident, $method:ident for $t:ty, $u:ty) => {
            forward_ref_op_assign!(impl $imp, $method for $t, $u,
                    #[stable(feature = "op_assign_builtins_by_ref", since = "1.22.0")]);
        };
        (impl $imp:ident, $method:ident for $t:ty, $u:ty, #[$attr:meta]) => {
            #[$attr]
            impl $imp<&$u> for $t {
                #[inline]
                fn $method(&mut self, other: &$u) {
                    $imp::$method(self, *other);
                }
            }
        }
    }

    /// Create a zero-size type similar to a closure type, but named.
    #[unstable(feature = "std_internals", issue = "none")]
    macro_rules! impl_fn_for_zst {
        ($(
            $( #[$attr: meta] )*
            struct $Name: ident impl$( <$( $lifetime : lifetime ),+> )? Fn =
                |$( $arg: ident: $ArgTy: ty ),*| -> $ReturnTy: ty
                $body: block;
        )+) => {
            $(
                $( #[$attr] )*
                struct $Name;

                impl $( <$( $lifetime ),+> )? Fn<($( $ArgTy, )*)> for $Name {
                    #[inline]
                    extern "rust-call" fn call(&self, ($( $arg, )*): ($( $ArgTy, )*)) -> $ReturnTy {
                        $body
                    }
                }

                impl $( <$( $lifetime ),+> )? FnMut<($( $ArgTy, )*)> for $Name {
                    #[inline]
                    extern "rust-call" fn call_mut(
                        &mut self,
                        ($( $arg, )*): ($( $ArgTy, )*)
                    ) -> $ReturnTy {
                        Fn::call(&*self, ($( $arg, )*))
                    }
                }

                impl $( <$( $lifetime ),+> )? FnOnce<($( $ArgTy, )*)> for $Name {
                    type Output = $ReturnTy;

                    #[inline]
                    extern "rust-call" fn call_once(self, ($( $arg, )*): ($( $ArgTy, )*)) -> $ReturnTy {
                        Fn::call(&self, ($( $arg, )*))
                    }
                }
            )+
        }
    }