# Struct rustc_infer::traits::Obligation

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    pub struct Obligation<'tcx, T> {
        pub cause: ObligationCause<'tcx>,
        pub param_env: ParamEnv<'tcx>,
        pub predicate: T,
        pub recursion_depth: usize,
    }

Expand description

An `Obligation` represents some trait reference (e.g., `i32: Eq`) for which the “impl_source” must be found. The process of finding an “impl_source” is called “resolving” the `Obligation`. This process consists of either identifying an `impl` (e.g., `impl Eq for i32`) that satisfies the obligation, or else finding a bound that is in scope. The eventual result is usually a `Selection` (defined below).

## Fields§

§`cause: ObligationCause<'tcx>`

The reason we have to prove this thing.

§`param_env: ParamEnv<'tcx>`

The environment in which we should prove this thing.

§`predicate: T`

The thing we are trying to prove.

§`recursion_depth: usize`

If we started proving this as a result of trying to prove something else, track the total depth to ensure termination. If this goes over a certain threshold, we abort compilation – in such cases, we can not say whether or not the predicate holds for certain. Stupid halting problem; such a drag.

## Implementations§

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### impl<'tcx> Obligation<'tcx, Predicate<'tcx>>

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#### pub fn flip_polarity( &self, tcx: TyCtxt<'tcx> ) -> Option<PredicateObligation<'tcx>>

Flips the polarity of the inner predicate.

Given `T: Trait` predicate it returns `T: !Trait` and given `T: !Trait` returns `T: Trait`.

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### impl<'tcx> Obligation<'tcx, Binder<'tcx, TraitPredicate<'tcx>>>

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#### pub fn derived_cause( &self, variant: impl FnOnce(DerivedObligationCause<'tcx>) -> ObligationCauseCode<'tcx> ) -> ObligationCause<'tcx>

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### impl<'tcx, O> Obligation<'tcx, O>

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#### pub fn new( tcx: TyCtxt<'tcx>, cause: ObligationCause<'tcx>, param_env: ParamEnv<'tcx>, predicate: impl ToPredicate<'tcx, O> ) -> Obligation<'tcx, O>

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#### pub fn set_depth_from_parent(&mut self, parent_depth: usize)

We often create nested obligations without setting the correct depth.

To deal with this evaluate and fulfill explicitly update the depth of nested obligations using this function.

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#### pub fn with_depth( tcx: TyCtxt<'tcx>, cause: ObligationCause<'tcx>, recursion_depth: usize, param_env: ParamEnv<'tcx>, predicate: impl ToPredicate<'tcx, O> ) -> Obligation<'tcx, O>

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#### pub fn misc( tcx: TyCtxt<'tcx>, span: Span, body_id: LocalDefId, param_env: ParamEnv<'tcx>, trait_ref: impl ToPredicate<'tcx, O> ) -> Obligation<'tcx, O>

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#### pub fn with<P>( &self, tcx: TyCtxt<'tcx>, value: impl ToPredicate<'tcx, P> ) -> Obligation<'tcx, P>

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### impl<'tcx> Obligation<'tcx, Binder<'tcx, TraitPredicate<'tcx>>>

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#### pub fn polarity(&self) -> ImplPolarity

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#### pub fn self_ty(&self) -> Binder<'tcx, Ty<'tcx>>

## Trait Implementations§

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### impl<'tcx, T: Clone> Clone for Obligation<'tcx, T>

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#### fn clone(&self) -> Obligation<'tcx, T>

Returns a copy of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl<'tcx, O: Debug> Debug for Obligation<'tcx, O>

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

Formats the value using the given formatter. Read more
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### impl<'tcx, P> From<Obligation<'tcx, P>> for Goal<'tcx, P>

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#### fn from(value: Obligation<'tcx, P>) -> Self

Converts to this type from the input type.
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### impl<T: Hash> Hash for Obligation<'_, T>

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

Feeds this value into the given `Hasher`. Read more
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#### fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
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### impl<'tcx, T: PartialEq> PartialEq for Obligation<'tcx, T>

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#### fn eq(&self, other: &Obligation<'tcx, T>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
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#### 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.
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### impl<'tcx, O: TypeFoldable<TyCtxt<'tcx>>> TypeFoldable<TyCtxt<'tcx>> for Obligation<'tcx, O>

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#### fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>( self, folder: &mut F ) -> Result<Self, F::Error>

The entry point for folding. To fold a value `t` with a folder `f` call: `t.try_fold_with(f)`. Read more
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#### fn fold_with<F>(self, folder: &mut F) -> Self
where F: TypeFolder<I>,

A convenient alternative to `try_fold_with` for use with infallible folders. Do not override this method, to ensure coherence with `try_fold_with`.
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### impl<'tcx, O: TypeVisitable<TyCtxt<'tcx>>> TypeVisitable<TyCtxt<'tcx>> for Obligation<'tcx, O>

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

The entry point for visiting. To visit a value `t` with a visitor `v` call: `t.visit_with(v)`. Read more
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### impl<T: Eq> Eq for Obligation<'_, T>

## Auto Trait Implementations§

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### impl<'tcx, T> !RefUnwindSafe for Obligation<'tcx, T>

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### impl<'tcx, T> Send for Obligation<'tcx, T>
where T: Send,

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### impl<'tcx, T> Sync for Obligation<'tcx, T>
where T: Sync,

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### impl<'tcx, T> Unpin for Obligation<'tcx, T>
where T: Unpin,

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### impl<'tcx, T> !UnwindSafe for Obligation<'tcx, T>

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.

## 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.