[][src]Struct rustc_mir::hair::pattern::_match::Witness

pub struct Witness<'tcx>(Vec<Pattern<'tcx>>);
🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

A witness of non-exhaustiveness for error reporting, represented as a list of patterns (in reverse order of construction) with wildcards inside to represent elements that can take any inhabitant of the type as a value.

A witness against a list of patterns should have the same types and length as the pattern matched against. Because Rust match is always against a single pattern, at the end the witness will have length 1, but in the middle of the algorithm, it can contain multiple patterns.

For example, if we are constructing a witness for the match against

struct Pair(Option<(u32, u32)>, bool);

match (p: Pair) {
   Pair(None, _) => {}
   Pair(_, false) => {}
}

We'll perform the following steps:

  1. Start with an empty witness Witness(vec![])
  2. Push a witness Some(_) against the None Witness(vec![Some(_)])
  3. Push a witness true against the false Witness(vec![Some(_), true])
  4. Apply the Pair constructor to the witnesses Witness(vec![Pair(Some(_), true)])

The final Pair(Some(_), true) is then the resulting witness.

Methods

impl<'tcx> Witness<'tcx>
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🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

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

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

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

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

Constructs a partial witness for a pattern given a list of patterns expanded by the specialization step.

When a pattern P is discovered to be useful, this function is used bottom-up to reconstruct a complete witness, e.g. a pattern P' that covers a subset of values, V, where each value in that set is not covered by any previously used patterns and is covered by the pattern P'. Examples:

left_ty: tuple of 3 elements pats: [10, 20, _] => (10, 20, _)

left_ty: struct X { a: (bool, &'static str), b: usize} pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }

Trait Implementations

impl<'tcx> Clone for Witness<'tcx>
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Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl<'tcx> Debug for Witness<'tcx>
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Formats the value using the given formatter. Read more

Auto Trait Implementations

impl<'tcx> !Send for Witness<'tcx>

impl<'tcx> !Sync for Witness<'tcx>

Blanket Implementations

impl<T> ToOwned for T where
    T: Clone
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Creates owned data from borrowed data, usually by cloning. Read more

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

recently added

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

impl<T> From for T
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Performs the conversion.

impl<T, U> Into for T where
    U: From<T>, 
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Performs the conversion.

impl<T, U> TryFrom for T where
    T: From<U>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

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

Performs the conversion.

impl<T> Borrow for T where
    T: ?Sized
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Important traits for &'a mut R

Immutably borrows from an owned value. Read more

impl<T, U> TryInto for T where
    U: TryFrom<T>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

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

Performs the conversion.

impl<T> BorrowMut for T where
    T: ?Sized
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Important traits for &'a mut R

Mutably borrows from an owned value. Read more

impl<T> Any for T where
    T: 'static + ?Sized
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🔬 This is a nightly-only experimental API. (get_type_id)

this method will likely be replaced by an associated static

Gets the TypeId of self. Read more

impl<E> SpecializationError for E
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🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

Create an error for a missing method specialization. Defaults to panicking with type, trait & method names. S is the encoder/decoder state type, T is the type being encoded/decoded, and the arguments are the names of the trait and method that should've been overridden. Read more

impl<T> Erased for T
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impl<T> Send for T where
    T: ?Sized
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impl<T> Sync for T where
    T: ?Sized
[src]

impl<T> Erased for T

impl<T> MaybeResult for T
[src]

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

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

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

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

impl<'a, T> Captures for T where
    T: ?Sized
[src]