Struct rustc_middle::ty::sty::ClosureSubsts[][src]

pub struct ClosureSubsts<'tcx> {
    pub substs: SubstsRef<'tcx>,

A closure can be modeled as a struct that looks like:

struct Closure<'l0...'li, T0...Tj, CK, CS, U>(...U);


So, for example, given this function:

fn foo<'a, T>(data: &'a mut T) {
     do(|| data.count += 1)

the type of the closure would be something like:

struct Closure<'a, T, U>(...U);

Note that the type of the upvar is not specified in the struct. You may wonder how the impl would then be able to use the upvar, if it doesn’t know it’s type? The answer is that the impl is (conceptually) not fully generic over Closure but rather tied to instances with the expected upvar types:

impl<'b, 'a, T> FnMut() for Closure<'a, T, (&'b mut &'a mut T,)> {

You can see that the impl fully specified the type of the upvar and thus knows full well that data has type &'b mut &'a mut T. (Here, I am assuming that data is mut-borrowed.)

Now, the last question you may ask is: Why include the upvar types in an extra type parameter? The reason for this design is that the upvar types can reference lifetimes that are internal to the creating function. In my example above, for example, the lifetime 'b represents the scope of the closure itself; this is some subset of foo, probably just the scope of the call to the to do(). If we just had the lifetime/type parameters from the enclosing function, we couldn’t name this lifetime 'b. Note that there can also be lifetimes in the types of the upvars themselves, if one of them happens to be a reference to something that the creating fn owns.

OK, you say, so why not create a more minimal set of parameters that just includes the extra lifetime parameters? The answer is primarily that it would be hard — we don’t know at the time when we create the closure type what the full types of the upvars are, nor do we know which are borrowed and which are not. In this design, we can just supply a fresh type parameter and figure that out later.

All right, you say, but why include the type parameters from the original function then? The answer is that codegen may need them when monomorphizing, and they may not appear in the upvars. A closure could capture no variables but still make use of some in-scope type parameter with a bound (e.g., if our example above had an extra U: Default, and the closure called U::default()).

There is another reason. This design (implicitly) prohibits closures from capturing themselves (except via a trait object). This simplifies closure inference considerably, since it means that when we infer the kind of a closure or its upvars, we don’t have to handle cycles where the decisions we make for closure C wind up influencing the decisions we ought to make for closure C (which would then require fixed point iteration to handle). Plus it fixes an ICE. :P


Generators are handled similarly in GeneratorSubsts. The set of type parameters is similar, but CK and CS are replaced by the following type parameters:


substs: SubstsRef<'tcx>

Lifetime and type parameters from the enclosing function, concatenated with a tuple containing the types of the upvars.

These are separated out because codegen wants to pass them around when monomorphizing.


impl<'tcx> ClosureSubsts<'tcx>[src]

pub fn new(
    tcx: TyCtxt<'tcx>,
    parts: ClosureSubstsParts<'tcx, Ty<'tcx>>
) -> ClosureSubsts<'tcx>

Construct ClosureSubsts from ClosureSubstsParts, containing Substs for the closure parent, alongside additional closure-specific components.

fn split(self) -> ClosureSubstsParts<'tcx, GenericArg<'tcx>>[src]

Divides the closure substs into their respective components. The ordering assumed here must match that used by ClosureSubsts::new above.

pub fn is_valid(self) -> bool[src]

Returns true only if enough of the synthetic types are known to allow using all of the methods on ClosureSubsts without panicking.

Used primarily by ty::print::pretty to be able to handle closure types that haven’t had their synthetic types substituted in.

pub fn parent_substs(self) -> &'tcx [GenericArg<'tcx>]

Notable traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

Returns the substitutions of the closure’s parent.

pub fn upvar_tys(self) -> impl Iterator<Item = Ty<'tcx>> + 'tcx[src]

Returns an iterator over the list of types of captured paths by the closure. In case there was a type error in figuring out the types of the captured path, an empty iterator is returned.

pub fn tupled_upvars_ty(self) -> Ty<'tcx>[src]

Returns the tuple type representing the upvars for this closure.

pub fn kind_ty(self) -> Ty<'tcx>[src]

Returns the closure kind for this closure; may return a type variable during inference. To get the closure kind during inference, use infcx.closure_kind(substs).

pub fn sig_as_fn_ptr_ty(self) -> Ty<'tcx>[src]

Returns the fn pointer type representing the closure signature for this closure.

pub fn kind(self) -> ClosureKind[src]

Returns the closure kind for this closure; only usable outside of an inference context, because in that context we know that there are no type variables.

If you have an inference context, use infcx.closure_kind().

pub fn sig(self) -> PolyFnSig<'tcx>[src]

Extracts the signature from the closure.

Trait Implementations

impl<'tcx> Clone for ClosureSubsts<'tcx>[src]

impl<'tcx> Copy for ClosureSubsts<'tcx>[src]

impl<'tcx> Debug for ClosureSubsts<'tcx>[src]

impl<'a, 'tcx> Lift<'tcx> for ClosureSubsts<'a>[src]

type Lifted = ClosureSubsts<'tcx>

impl<'tcx> Relate<'tcx> for ClosureSubsts<'tcx>[src]

impl<'tcx> TypeFoldable<'tcx> for ClosureSubsts<'tcx>[src]

Auto Trait Implementations

impl<'tcx> !RefUnwindSafe for ClosureSubsts<'tcx>

impl<'tcx> !Send for ClosureSubsts<'tcx>

impl<'tcx> !Sync for ClosureSubsts<'tcx>

impl<'tcx> Unpin for ClosureSubsts<'tcx>

impl<'tcx> !UnwindSafe for ClosureSubsts<'tcx>

Blanket Implementations

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

impl<'tcx, T> ArenaAllocatable<'tcx, ()> for T where
    T: Copy

impl<T> Borrow<T> for T where
    T: ?Sized

impl<T> BorrowMut<T> for T where
    T: ?Sized

impl<'a, T> Captures<'a> for T where
    T: ?Sized

impl<T> From<T> for T[src]

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

impl<T> MaybeResult<T> for T[src]

type Error = !

impl<'tcx, T> Subst<'tcx> for T where
    T: TypeFoldable<'tcx>, 

impl<T> ToOwned for T where
    T: Clone

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 

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

The type returned in the event of a conversion error.

impl<T> WithConstness for T[src]