Struct rustc_middle::ty::WithOptConstParam

pub struct WithOptConstParam<T> {
    pub did: T,
    pub const_param_did: Option<DefId>,
}

A DefId which, in case it is a const argument, is potentially bundled with the DefId of the generic parameter it instantiates.

This is used to avoid calls to type_of for const arguments during typeck which cause cycle errors.

struct A;
impl A {
    fn foo<const N: usize>(&self) -> [u8; N] { [0; N] }
    //           ^ const parameter
}
struct B;
impl B {
    fn foo<const M: u8>(&self) -> usize { 42 }
    //           ^ const parameter
}

fn main() {
    let a = A;
    let _b = a.foo::<{ 3 + 7 }>();
    //               ^^^^^^^^^ const argument
}

Let’s look at the call a.foo::<{ 3 + 7 }>() here. We do not know which foo is used until we know the type of a.

We only know the type of a once we are inside of typeck(main). We also end up normalizing the type of _b during typeck(main) which requires us to evaluate the const argument.

To evaluate that const argument we need to know its type, which we would get using type_of(const_arg). This requires us to resolve foo as it can be either usize or u8 in this example. However, resolving foo once again requires typeck(main) to get the type of a, which results in a cycle.

In short we must not call type_of(const_arg) during typeck(main).

When first creating the ty::Const of the const argument inside of typeck we have already resolved foo so we know which const parameter this argument instantiates. This means that we also know the expected result of type_of(const_arg) even if we aren’t allowed to call that query: it is equal to type_of(const_param) which is trivial to compute.

If we now want to use that constant in a place which potentionally needs its type we also pass the type of its const_param. This is the point of WithOptConstParam, except that instead of a Ty we bundle the DefId of the const parameter. Meaning that we need to use type_of(const_param_did) if const_param_did is Some to get the type of did.

Fields

did: T

const_param_did: Option<DefId>

The DefId of the corresponding generic parameter in case did is a const argument.

Note that even if did is a const argument, this may still be None. All queries taking WithOptConstParam start by calling tcx.opt_const_param_of(def.did) to potentially update param_did in the case it is None.

Implementations

impl<T> WithOptConstParam<T>

pub fn unknown(did: T) -> WithOptConstParam<T>

Creates a new WithOptConstParam setting const_param_did to None.

impl WithOptConstParam<LocalDefId>

pub fn try_lookup(
    did: LocalDefId,
    tcx: TyCtxt<'_>
) -> Option<(LocalDefId, DefId)>

Returns Some((did, param_did)) if def_id is a const argument, None otherwise.

pub fn try_upgrade(
    self,
    tcx: TyCtxt<'_>
) -> Option<WithOptConstParam<LocalDefId>>

In case self is unknown but self.did is a const argument, this returns a WithOptConstParam with the correct const_param_did.

pub fn to_global(self) -> WithOptConstParam<DefId>

pub fn def_id_for_type_of(self) -> DefId

impl WithOptConstParam<DefId>

pub fn as_local(self) -> Option<WithOptConstParam<LocalDefId>>

pub fn as_const_arg(self) -> Option<(LocalDefId, DefId)>

pub fn is_local(self) -> bool

pub fn def_id_for_type_of(self) -> DefId

Trait Implementations

impl<T: Clone> Clone for WithOptConstParam<T>

fn clone(&self) -> WithOptConstParam<T>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug> Debug for WithOptConstParam<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'tcx, T, __D: TyDecoder<'tcx>> Decodable<__D> for WithOptConstParam<T> where
    T: Decodable<__D>, 

fn decode(__decoder: &mut __D) -> Result<Self, <__D as Decoder>::Error>

impl<'tcx, T, __E: TyEncoder<'tcx>> Encodable<__E> for WithOptConstParam<T> where
    T: Encodable<__E>, 

fn encode(&self, __encoder: &mut __E) -> Result<(), <__E as Encoder>::Error>

impl<T: Hash> Hash for WithOptConstParam<T>

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

Feeds this value into the given Hasher.

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

Feeds a slice of this type into the given Hasher.

impl<'__ctx, T> HashStable<StableHashingContext<'__ctx>> for WithOptConstParam<T> where
    T: HashStable<StableHashingContext<'__ctx>>, 

fn hash_stable(
    &self,
    __hcx: &mut StableHashingContext<'__ctx>,
    __hasher: &mut StableHasher
)

impl<'__lifted, T> Lift<'__lifted> for WithOptConstParam<T> where
    T: Lift<'__lifted>, 

type Lifted = WithOptConstParam<T::Lifted>

fn lift_to_tcx(
    self,
    __tcx: TyCtxt<'__lifted>
) -> Option<WithOptConstParam<T::Lifted>>

impl<T: Ord> Ord for WithOptConstParam<T>

fn cmp(&self, other: &WithOptConstParam<T>) -> Ordering

This method returns an Ordering between self and other.

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

Compares and returns the maximum of two values.

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

Compares and returns the minimum of two values.

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

Restrict a value to a certain interval.

impl<T: PartialEq> PartialEq<WithOptConstParam<T>> for WithOptConstParam<T>

fn eq(&self, other: &WithOptConstParam<T>) -> bool

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

fn ne(&self, other: &WithOptConstParam<T>) -> bool

This method tests for !=.

impl<T: PartialOrd> PartialOrd<WithOptConstParam<T>> for WithOptConstParam<T>

fn partial_cmp(&self, other: &WithOptConstParam<T>) -> 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<T, 'tcx> TypeFoldable<'tcx> for WithOptConstParam<T> where
    T: TypeFoldable<'tcx>, 

fn super_fold_with<__F: TypeFolder<'tcx>>(self, __folder: &mut __F) -> Self

fn super_visit_with<__F: TypeVisitor<'tcx>>(
    &self,
    __folder: &mut __F
) -> ControlFlow<__F::BreakTy>

fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self

fn visit_with<V: TypeVisitor<'tcx>>(
    &self,
    visitor: &mut V
) -> ControlFlow<V::BreakTy>

fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool

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.

fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool

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

fn has_escaping_bound_vars(&self) -> bool

fn definitely_has_type_flags(&self, tcx: TyCtxt<'tcx>, flags: TypeFlags) -> bool

fn has_type_flags(&self, flags: TypeFlags) -> bool

fn has_projections(&self) -> bool

fn has_opaque_types(&self) -> bool

fn references_error(&self) -> bool

fn potentially_has_param_types_or_consts(&self) -> bool

fn definitely_has_param_types_or_consts(&self, tcx: TyCtxt<'tcx>) -> bool

fn has_infer_regions(&self) -> bool

fn has_infer_types(&self) -> bool

fn has_infer_types_or_consts(&self) -> bool

fn needs_infer(&self) -> bool

fn has_placeholders(&self) -> bool

fn potentially_needs_subst(&self) -> bool

fn definitely_needs_subst(&self, tcx: TyCtxt<'tcx>) -> bool

fn has_free_regions(&self, tcx: TyCtxt<'tcx>) -> bool

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

fn has_erased_regions(&self) -> bool

fn has_erasable_regions(&self, tcx: TyCtxt<'tcx>) -> bool

True if there are any un-erased free regions.

fn is_known_global(&self) -> bool

Indicates whether this value definitely references only ‘global’ generic parameters that are the same regardless of what fn we are in. This is used for caching.

fn is_global(&self, tcx: TyCtxt<'tcx>) -> bool

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.

fn has_late_bound_regions(&self) -> bool

True if there are any late-bound regions

fn still_further_specializable(&self) -> bool

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.

impl<T: Copy> Copy for WithOptConstParam<T>

impl<T: Eq> Eq for WithOptConstParam<T>

impl<T> StructuralEq for WithOptConstParam<T>

impl<T> StructuralPartialEq for WithOptConstParam<T>

Layout

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.