pub struct UniverseIndex {
    pub(crate) private: u32,
}
Expand description

“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

Maximum value the index can take, as a u32.

Maximum value the index can take.

Creates a new index from a given usize.

Panics

Will panic if value exceeds MAX.

Creates a new index from a given u32.

Panics

Will panic if value exceeds MAX.

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.

Extracts the value of this index as a usize.

Extracts the value of this index as a u32.

Extracts the value of this index as a usize.

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.

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).

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

The resulting type after applying the + operator.

Performs the + operation. Read more

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Converts to this type from the input type.

Converts to this type from the input type.

Converts to this type from the input type.

Converts to this type from the input type.

Feeds this value into the given Hasher. Read more

Feeds a slice of this type into the given Hasher. Read more

This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

Restrict a value to a certain interval. Read more

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

This method tests for !=.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

Uses borrowed data to replace owned data, usually by cloning. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

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