Struct rustc_middle::ty::UniverseIndex

pub struct UniverseIndex {
    pub(crate) private_use_as_methods_instead: 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_use_as_methods_instead: u32

Implementations

impl UniverseIndex

pub const MAX_AS_U32: u32 = 4_294_967_040u32

Maximum value the index can take, as a u32.

pub const MAX: UniverseIndex = _

Maximum value the index can take.

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

Creates a new index from a given usize.

Panics

Will panic if value exceeds MAX.

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

Creates a new index from a given u32.

Panics

Will panic if value exceeds MAX.

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

Creates a new index from a given u32.

Safety

The provided value must be less than or equal to the maximum value for the newtype. Providing a value outside this range is undefined due to layout restrictions.

Prefer using from_u32.

pub const fn index(self) -> usize

Extracts the value of this index as a usize.

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 = UniverseIndex

The resulting type after applying the + operator.

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

Performs the + operation.

impl Clone for UniverseIndex

fn clone(&self) -> UniverseIndex

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<(), Error>

Formats the value using the given formatter.

impl<D> Decodable<D> for UniverseIndex

where D: Decoder,

fn decode(d: &mut D) -> UniverseIndex

impl Default for UniverseIndex

fn default() -> UniverseIndex

Returns the “default value” for a type.

impl<E> Encodable<E> for UniverseIndex

where E: Encoder,

fn encode(&self, e: &mut E)

impl From<u32> for UniverseIndex

fn from(value: u32) -> UniverseIndex

Converts to this type from the input type.

impl From<usize> for UniverseIndex

fn from(value: usize) -> UniverseIndex

Converts to this type from the input type.

impl Hash for UniverseIndex

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

where __H: Hasher,

Feeds this value into the given Hasher.

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

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<__CTX> HashStable<__CTX> for UniverseIndex

fn hash_stable(&self, __hcx: &mut __CTX, __hasher: &mut StableHasher)

impl Idx for UniverseIndex

fn new(value: usize) -> UniverseIndex

fn index(self) -> usize

fn increment_by(&mut self, amount: usize)

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

impl Ord for UniverseIndex

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

This method returns an Ordering between self and other.

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

where Self: Sized,

Compares and returns the maximum of two values.

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

where Self: Sized,

Compares and returns the minimum of two values.

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

where Self: Sized + PartialOrd,

Restrict a value to a certain interval.

impl PartialEq 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: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for UniverseIndex

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

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

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

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

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

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

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

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

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: &UniverseIndex, end: &UniverseIndex) -> Option<usize>

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

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

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

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

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

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

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

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)

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)

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)

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)

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

impl<I> TypeFoldable<I> for UniverseIndex

where I: Interner,

fn try_fold_with<F>( self, _: &mut F ) -> Result<UniverseIndex, <F as FallibleTypeFolder<I>>::Error>

where F: FallibleTypeFolder<I>,

The entry point for folding. To fold a value t with a folder f call: t.try_fold_with(f).

fn fold_with<F>(self, _: &mut F) -> UniverseIndex

where F: TypeFolder<I>,

A convenient alternative to try_fold_with for use with infallible folders. Do not override this method, to ensure coherence with try_fold_with.

impl<I> TypeVisitable<I> for UniverseIndex

where I: Interner,

fn visit_with<F>(&self, _: &mut F) -> <F as TypeVisitor<I>>::Result

where F: TypeVisitor<I>,

The entry point for visiting. To visit a value t with a visitor v call: t.visit_with(v).

impl Copy for UniverseIndex

impl Eq for UniverseIndex

impl StructuralPartialEq for UniverseIndex

impl TrustedStep for UniverseIndex

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 4 bytes