Enum rustc_trait_selection::solve::CandidateSource

pub enum CandidateSource<I>
where
    I: Interner,
{
    Impl(<I as Interner>::DefId),
    BuiltinImpl(BuiltinImplSource),
    ParamEnv(usize),
    AliasBound,
    CoherenceUnknowable,
}

Possible ways the given goal can be proven.

Variants

Impl(<I as Interner>::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<I> Clone for CandidateSource<I>

where I: Interner,

fn clone(&self) -> CandidateSource<I>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<I> Debug for CandidateSource<I>

where I: Interner,

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

Formats the value using the given formatter.

impl<I> Hash for CandidateSource<I>

where I: Interner,

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

where __H: Hasher,

Feeds this value into the given Hasher.

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

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<I> PartialEq for CandidateSource<I>

where I: Interner,

fn eq(&self, __other: &CandidateSource<I>) -> bool

Tests for self and other values to be equal, and is used by ==.

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

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

impl<I> Copy for CandidateSource<I>

where I: Interner,

impl<I> Eq for CandidateSource<I>

where I: Interner,

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.