Enum rustc_trait_selection::traits::ImplSource

pub enum ImplSource<'tcx, N> {
    UserDefined(ImplSourceUserDefinedData<'tcx, N>),
    AutoImpl(ImplSourceAutoImplData<N>),
    Param(Vec<N, Global>, BoundConstness),
    Object(ImplSourceObjectData<'tcx, N>),
    Builtin(ImplSourceBuiltinData<N>),
    TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>),
    Closure(ImplSourceClosureData<'tcx, N>),
    FnPointer(ImplSourceFnPointerData<'tcx, N>),
    DiscriminantKind(ImplSourceDiscriminantKindData),
    Pointee(ImplSourcePointeeData),
    Generator(ImplSourceGeneratorData<'tcx, N>),
    TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
    ConstDestruct(ImplSourceConstDestructData<N>),
    Tuple,
}

Given the successful resolution of an obligation, the ImplSource indicates where the impl comes from.

For example, the obligation may be satisfied by a specific impl (case A), or it may be relative to some bound that is in scope (case B).

impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
impl Clone for i32 { ... }                   // Impl_3

fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
    // Case A: ImplSource points at a specific impl. Only possible when
    // type is concretely known. If the impl itself has bounded
    // type parameters, ImplSource will carry resolutions for those as well:
    concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])

    // Case A: ImplSource points at a specific impl. Only possible when
    // type is concretely known. If the impl itself has bounded
    // type parameters, ImplSource will carry resolutions for those as well:
    concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])

    // Case B: ImplSource must be provided by caller. This applies when
    // type is a type parameter.
    param.clone();    // ImplSource::Param

    // Case C: A mix of cases A and B.
    mixed.clone();    // ImplSource(Impl_1, [ImplSource::Param])
}

The type parameter N

See explanation on ImplSourceUserDefinedData.

Variants

UserDefined(ImplSourceUserDefinedData<'tcx, N>)

ImplSource identifying a particular impl.

AutoImpl(ImplSourceAutoImplData<N>)

ImplSource for auto trait implementations. This carries the information and nested obligations with regards to an auto implementation for a trait Trait. The nested obligations ensure the trait implementation holds for all the constituent types.

Param(Vec<N, Global>, BoundConstness)

Successful resolution to an obligation provided by the caller for some type parameter. The Vec<N> represents the obligations incurred from normalizing the where-clause (if any).

Object(ImplSourceObjectData<'tcx, N>)

Virtual calls through an object.

Builtin(ImplSourceBuiltinData<N>)

Successful resolution for a builtin trait.

TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>)

ImplSource for trait upcasting coercion

Closure(ImplSourceClosureData<'tcx, N>)

ImplSource automatically generated for a closure. The DefId is the ID of the closure expression. This is an ImplSource::UserDefined in spirit, but the impl is generated by the compiler and does not appear in the source.

FnPointer(ImplSourceFnPointerData<'tcx, N>)

Same as above, but for a function pointer type with the given signature.

DiscriminantKind(ImplSourceDiscriminantKindData)

ImplSource for a builtin DeterminantKind trait implementation.

Pointee(ImplSourcePointeeData)

ImplSource for a builtin Pointee trait implementation.

Generator(ImplSourceGeneratorData<'tcx, N>)

ImplSource automatically generated for a generator.

TraitAlias(ImplSourceTraitAliasData<'tcx, N>)

ImplSource for a trait alias.

ConstDestruct(ImplSourceConstDestructData<N>)

ImplSource for a const Drop implementation.

Tuple

ImplSource for a std::marker::Tuple implementation. This has no nested predicates ever, so no data.

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: 72 bytes

Size for each variant:

• UserDefined: 47 bytes
• AutoImpl: 39 bytes
• Param: 31 bytes
• Object: 63 bytes
• Builtin: 31 bytes
• TraitUpcasting: 71 bytes
• Closure: 47 bytes
• FnPointer: 39 bytes
• DiscriminantKind: 0 bytes
• Pointee: 0 bytes
• Generator: 47 bytes
• TraitAlias: 47 bytes
• ConstDestruct: 31 bytes
• Tuple: 0 bytes