Enum rustc_typeck::check::Expectation [−][src]
pub enum Expectation<'tcx> { NoExpectation, ExpectIfCondition, ExpectHasType(Ty<'tcx>), ExpectCastableToType(Ty<'tcx>), ExpectRvalueLikeUnsized(Ty<'tcx>), }
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)
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When type-checking an expression, we propagate downward
whatever type hint we are able in the form of an Expectation
.
Variants
NoExpectation
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We know nothing about what type this expression should have.
ExpectIfCondition
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This expression is an if
condition, it must resolve to bool
.
ExpectHasType(Ty<'tcx>)
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This expression should have the type given (or some subtype)
ExpectCastableToType(Ty<'tcx>)
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This expression will be cast to the Ty
ExpectRvalueLikeUnsized(Ty<'tcx>)
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This rvalue expression will be wrapped in &
or Box
and coerced
to &Ty
or Box<Ty>
, respectively. Ty
is [A]
or Trait
.
Methods
impl<'a, 'gcx, 'tcx> Expectation<'tcx>
[src]
impl<'a, 'gcx, 'tcx> Expectation<'tcx>
fn adjust_for_branches(&self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Expectation<'tcx>
[src]
fn adjust_for_branches(&self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Expectation<'tcx>
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)
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fn rvalue_hint(fcx: &FnCtxt<'a, 'gcx, 'tcx>, ty: Ty<'tcx>) -> Expectation<'tcx>
[src]
fn rvalue_hint(fcx: &FnCtxt<'a, 'gcx, 'tcx>, ty: Ty<'tcx>) -> Expectation<'tcx>
🔬 This is a nightly-only experimental API. (rustc_private
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Provide an expectation for an rvalue expression given an optional
hint, which is not required for type safety (the resulting type might
be checked higher up, as is the case with &expr
and box expr
), but
is useful in determining the concrete type.
The primary use case is where the expected type is a fat pointer,
like &[isize]
. For example, consider the following statement:
let x: &[isize] = &[1, 2, 3];
In this case, the expected type for the &[1, 2, 3]
expression is
&[isize]
. If however we were to say that [1, 2, 3]
has the
expectation ExpectHasType([isize])
, that would be too strong --
[1, 2, 3]
does not have the type [isize]
but rather [isize; 3]
.
It is only the &[1, 2, 3]
expression as a whole that can be coerced
to the type &[isize]
. Therefore, we propagate this more limited hint,
which still is useful, because it informs integer literals and the like.
See the test case test/run-pass/coerce-expect-unsized.rs
and #20169
for examples of where this comes up,.
fn resolve(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Expectation<'tcx>
[src]
fn resolve(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Expectation<'tcx>
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fn to_option(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Option<Ty<'tcx>>
[src]
fn to_option(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Option<Ty<'tcx>>
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fn only_has_type(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Option<Ty<'tcx>>
[src]
fn only_has_type(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Option<Ty<'tcx>>
🔬 This is a nightly-only experimental API. (rustc_private
)
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It sometimes happens that we want to turn an expectation into
a hard constraint (i.e., something that must be satisfied
for the program to type-check). only_has_type
will return
such a constraint, if it exists.
fn coercion_target_type(
self,
fcx: &FnCtxt<'a, 'gcx, 'tcx>,
span: Span
) -> Ty<'tcx>
[src]
fn coercion_target_type(
self,
fcx: &FnCtxt<'a, 'gcx, 'tcx>,
span: Span
) -> Ty<'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?
Like only_has_type
, but instead of returning None
if no
hard constraint exists, creates a fresh type variable.
Trait Implementations
impl<'tcx> Copy for Expectation<'tcx>
[src]
impl<'tcx> Copy for Expectation<'tcx>
impl<'tcx> Clone for Expectation<'tcx>
[src]
impl<'tcx> Clone for Expectation<'tcx>
fn clone(&self) -> Expectation<'tcx>
[src]
fn clone(&self) -> Expectation<'tcx>
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)
1.0.0[src]
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source
. Read more
impl<'tcx> Debug for Expectation<'tcx>
[src]
impl<'tcx> Debug for Expectation<'tcx>
Auto Trait Implementations
impl<'tcx> !Send for Expectation<'tcx>
impl<'tcx> !Send for Expectation<'tcx>
impl<'tcx> !Sync for Expectation<'tcx>
impl<'tcx> !Sync for Expectation<'tcx>