Enum rustc_middle::mir::FakeReadCause[][src]

pub enum FakeReadCause {
    ForMatchGuard,
    ForMatchedPlace(Option<DefId>),
    ForGuardBinding,
    ForLet(Option<DefId>),
    ForIndex,
}
Expand description

The FakeReadCause describes the type of pattern why a FakeRead statement exists.

Variants

ForMatchGuard

Inject a fake read of the borrowed input at the end of each guards code.

This should ensure that you cannot change the variant for an enum while you are in the midst of matching on it.

ForMatchedPlace(Option<DefId>)

let x: !; match x {} doesn’t generate any read of x so we need to generate a read of x to check that it is initialized and safe.

If a closure pattern matches a Place starting with an Upvar, then we introduce a FakeRead for that Place outside the closure, in such a case this option would be Some(closure_def_id). Otherwise, the value of the optional DefId will be None.

ForGuardBinding

A fake read of the RefWithinGuard version of a bind-by-value variable in a match guard to ensure that it’s value hasn’t change by the time we create the OutsideGuard version.

ForLet(Option<DefId>)

Officially, the semantics of

let pattern = <expr>;

is that <expr> is evaluated into a temporary and then this temporary is into the pattern.

However, if we see the simple pattern let var = <expr>, we optimize this to evaluate <expr> directly into the variable var. This is mostly unobservable, but in some cases it can affect the borrow checker, as in #53695. Therefore, we insert a “fake read” here to ensure that we get appropriate errors.

If a closure pattern matches a Place starting with an Upvar, then we introduce a FakeRead for that Place outside the closure, in such a case this option would be Some(closure_def_id). Otherwise, the value of the optional DefId will be None.

ForIndex

If we have an index expression like

(*x)[1][{ x = y; 4}]

then the first bounds check is invalidated when we evaluate the second index expression. Thus we create a fake borrow of x across the second indexer, which will cause a borrow check error.

Trait Implementations

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Feeds this value into the given Hasher. Read more

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

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

This method tests for !=.

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. Read more

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

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

True if there are any un-erased free regions.

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. Read more

True if there are any late-bound regions

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. 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

Performs the conversion.

Performs the conversion.

The resulting type after obtaining ownership.

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

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 be different between compiler versions and platforms. 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: 12 bytes