Enum rustc_trait_selection::traits::solve::CandidateSource

pub enum CandidateSource {
    Impl(DefId),
    BuiltinImpl(BuiltinImplSource),
    ParamEnv(usize),
    AliasBound,
    CoherenceUnknowable,
}

Possible ways the given goal can be proven.

Variants

Impl(DefId)

A user written impl.

Examples

fn main() {
    let x: Vec<u32> = Vec::new();
    // This uses the impl from the standard library to prove `Vec<T>: Clone`.
    let y = x.clone();
}

BuiltinImpl(BuiltinImplSource)

A builtin impl generated by the compiler. When adding a new special trait, try to use actual impls whenever possible. Builtin impls should only be used in cases where the impl cannot be manually be written.

Notable examples are auto traits, Sized, and DiscriminantKind. For a list of all traits with builtin impls, check out the EvalCtxt::assemble_builtin_impl_candidates method.

ParamEnv(usize)

An assumption from the environment.

More precisely we’ve used the n-th assumption in the param_env.

Examples

fn is_clone<T: Clone>(x: T) -> (T, T) {
    // This uses the assumption `T: Clone` from the `where`-bounds
    // to prove `T: Clone`.
    (x.clone(), x)
}

AliasBound

If the self type is an alias type, e.g. an opaque type or a projection, we know the bounds on that alias to hold even without knowing its concrete underlying type.

More precisely this candidate is using the n-th bound in the item_bounds of the self type.

Examples

trait Trait {
    type Assoc: Clone;
}

fn foo<T: Trait>(x: <T as Trait>::Assoc) {
    // We prove `<T as Trait>::Assoc` by looking at the bounds on `Assoc` in
    // in the trait definition.
    let _y = x.clone();
}

CoherenceUnknowable

A candidate that is registered only during coherence to represent some yet-unknown impl that could be produced downstream without violating orphan rules.

Trait Implementations

impl Clone for CandidateSource

fn clone(&self) -> CandidateSource

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for CandidateSource

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

Formats the value using the given formatter.

impl PartialEq for CandidateSource

fn eq(&self, other: &CandidateSource) -> bool

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

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for CandidateSource

impl Eq for CandidateSource

impl StructuralPartialEq for CandidateSource

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: 16 bytes

Size for each variant:

• Impl: 16 bytes
• BuiltinImpl: 16 bytes
• ParamEnv: 16 bytes
• AliasBound: 0 bytes
• CoherenceUnknowable: 0 bytes