Struct rustc_middle::ty::UniverseIndex

pub struct UniverseIndex {
    private: u32,
}

“Universes” are used during type- and trait-checking in the presence of for<..> binders to control what sets of names are visible. Universes are arranged into a tree: the root universe contains names that are always visible. Each child then adds a new set of names that are visible, in addition to those of its parent. We say that the child universe “extends” the parent universe with new names.

To make this more concrete, consider this program:

struct Foo { }
fn bar<T>(x: T) {
  let y: for<'a> fn(&'a u8, Foo) = ...;
}

The struct name Foo is in the root universe U0. But the type parameter T, introduced on bar, is in an extended universe U1 – i.e., within bar, we can name both T and Foo, but outside of bar, we cannot name T. Then, within the type of y, the region 'a is in a universe U2 that extends U1, because we can name it inside the fn type but not outside.

Universes are used to do type- and trait-checking around these “forall” binders (also called universal quantification). The idea is that when, in the body of bar, we refer to T as a type, we aren’t referring to any type in particular, but rather a kind of “fresh” type that is distinct from all other types we have actually declared. This is called a placeholder type, and we use universes to talk about this. In other words, a type name in universe 0 always corresponds to some “ground” type that the user declared, but a type name in a non-zero universe is a placeholder type – an idealized representative of “types in general” that we use for checking generic functions.

Fields

private: u32

Implementations

impl UniverseIndex

pub const MAX_AS_U32: u32

pub const MAX: Self

pub const fn from_usize(value: usize) -> Self

pub const fn from_u32(value: u32) -> Self

pub const unsafe fn from_u32_unchecked(value: u32) -> Self

pub const fn index(self) -> usize

Extracts the value of this index as an integer.

pub const fn as_u32(self) -> u32

Extracts the value of this index as a u32.

pub const fn as_usize(self) -> usize

Extracts the value of this index as a usize.

impl UniverseIndex

pub const ROOT: UniverseIndex

pub fn next_universe(self) -> UniverseIndex

Returns the “next” universe index in order – this new index is considered to extend all previous universes. This corresponds to entering a forall quantifier. So, for example, suppose we have this type in universe U:

for<'a> fn(&'a u32)

Once we “enter” into this for<'a> quantifier, we are in a new universe that extends U – in this new universe, we can name the region 'a, but that region was not nameable from U because it was not in scope there.

pub fn can_name(self, other: UniverseIndex) -> bool

Returns true if self can name a name from other – in other words, if the set of names in self is a superset of those in other (self >= other).

pub fn cannot_name(self, other: UniverseIndex) -> bool

Returns true if self cannot name some names from other – in other words, if the set of names in self is a strict subset of those in other (self < other).

Trait Implementations

impl Add<usize> for UniverseIndex

type Output = Self

The resulting type after applying the + operator.

fn add(self, other: usize) -> Self

Performs the + operation.

impl Clone for UniverseIndex

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for UniverseIndex

fn fmt(&self, fmt: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<D: Decoder> Decodable<D> for UniverseIndex

fn decode(d: &mut D) -> Result<Self, D::Error>

impl<E: Encoder> Encodable<E> for UniverseIndex

fn encode(&self, e: &mut E) -> Result<(), E::Error>

impl From<u32> for UniverseIndex

fn from(value: u32) -> Self

Performs the conversion.

impl From<usize> for UniverseIndex

fn from(value: usize) -> Self

Performs the conversion.

impl Hash for UniverseIndex

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given Hasher.

impl<'__ctx> HashStable<StableHashingContext<'__ctx>> for UniverseIndex

fn hash_stable(
    &self,
    __hcx: &mut StableHashingContext<'__ctx>,
    __hasher: &mut StableHasher
)

impl Idx for UniverseIndex

fn new(value: usize) -> Self

fn index(self) -> usize

fn increment_by(&mut self, amount: usize)

fn plus(self, amount: usize) -> Self

impl<'tcx> Lift<'tcx> for UniverseIndex

type Lifted = Self

fn lift_to_tcx(self, _: TyCtxt<'tcx>) -> Option<Self>

impl Ord for UniverseIndex

fn cmp(&self, other: &UniverseIndex) -> Ordering

This method returns an Ordering between self and other.

#[must_use]

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

#[must_use]

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

#[must_use]

fn clamp(self, min: Self, max: Self) -> Self

Restrict a value to a certain interval.

impl PartialEq<UniverseIndex> for UniverseIndex

fn eq(&self, other: &UniverseIndex) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &UniverseIndex) -> bool

This method tests for !=.

impl PartialOrd<UniverseIndex> for UniverseIndex

fn partial_cmp(&self, other: &UniverseIndex) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

#[must_use]

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

#[must_use]

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

#[must_use]

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

#[must_use]

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Step for UniverseIndex

fn steps_between(start: &Self, end: &Self) -> Option<usize>

🔬 This is a nightly-only experimental API. (step_trait)

recently redesigned

Returns the number of successor steps required to get from start to end.

fn forward_checked(start: Self, u: usize) -> Option<Self>

🔬 This is a nightly-only experimental API. (step_trait_ext)

recently added

Returns the value that would be obtained by taking the successor of self count times.

fn backward_checked(start: Self, u: usize) -> Option<Self>

🔬 This is a nightly-only experimental API. (step_trait_ext)

recently added

Returns the value that would be obtained by taking the predecessor of self count times.

fn forward(start: Self, count: usize) -> Self

🔬 This is a nightly-only experimental API. (step_trait_ext)

recently added

Returns the value that would be obtained by taking the successor of self count times.

unsafe fn forward_unchecked(start: Self, count: usize) -> Self

🔬 This is a nightly-only experimental API. (step_trait_ext)

recently added

Returns the value that would be obtained by taking the successor of self count times.

fn backward(start: Self, count: usize) -> Self

🔬 This is a nightly-only experimental API. (step_trait_ext)

recently added

Returns the value that would be obtained by taking the predecessor of self count times.

unsafe fn backward_unchecked(start: Self, count: usize) -> Self

🔬 This is a nightly-only experimental API. (step_trait_ext)

recently added

Returns the value that would be obtained by taking the predecessor of self count times.

impl<'tcx> TypeFoldable<'tcx> for UniverseIndex

fn super_fold_with<F: TypeFolder<'tcx>>(self, _: &mut F) -> UniverseIndex

fn super_visit_with<F: TypeVisitor<'tcx>>(
    &self,
    _: &mut F
) -> ControlFlow<F::BreakTy>

fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self

fn visit_with<V: TypeVisitor<'tcx>>(
    &self,
    visitor: &mut V
) -> ControlFlow<V::BreakTy>

fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool

Returns true if self has any late-bound regions that are either bound by binder or bound by some binder outside of binder. If binder is ty::INNERMOST, this indicates whether there are any late-bound regions that appear free.

fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool

Returns true if this self has any regions that escape binder (and hence are not bound by it).

fn has_escaping_bound_vars(&self) -> bool

fn has_type_flags(&self, flags: TypeFlags) -> bool

fn has_projections(&self) -> bool

fn has_opaque_types(&self) -> bool

fn references_error(&self) -> bool

fn has_param_types_or_consts(&self) -> bool

fn has_infer_regions(&self) -> bool

fn has_infer_types(&self) -> bool

fn has_infer_types_or_consts(&self) -> bool

fn needs_infer(&self) -> bool

fn has_placeholders(&self) -> bool

fn needs_subst(&self) -> bool

fn has_free_regions(&self) -> bool

“Free” regions in this context means that it has any region that is not (a) erased or (b) late-bound.

fn has_erased_regions(&self) -> bool

fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.

fn is_global(&self) -> bool

Indicates whether this value references only ‘global’ generic parameters that are the same regardless of what fn we are in. This is used for caching.

fn has_late_bound_regions(&self) -> bool

True if there are any late-bound regions

fn still_further_specializable(&self) -> bool

Indicates whether this value still has parameters/placeholders/inference variables which could be replaced later, in a way that would change the results of impl specialization.

impl Copy for UniverseIndex

impl Eq for UniverseIndex

impl StructuralEq for UniverseIndex

impl StructuralPartialEq for UniverseIndex