Struct rustc::mir::ClosureRegionRequirements

pub struct ClosureRegionRequirements {
    pub num_external_vids: usize,
    pub outlives_requirements: Vec<ClosureOutlivesRequirement>,
}

🔬 This is a nightly-only experimental API. (rustc_private)

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After we borrow check a closure, we are left with various requirements that we have inferred between the free regions that appear in the closure's signature or on its field types. These requirements are then verified and proved by the closure's creating function. This struct encodes those requirements.

The requirements are listed as being between various RegionVid. The 0th region refers to 'static; subsequent region vids refer to the free regions that appear in the closure (or generator's) type, in order of appearance. (This numbering is actually defined by the UniversalRegions struct in the NLL region checker. See for example UniversalRegions::closure_mapping.) Note that we treat the free regions in the closure's type "as if" they were erased, so their precise identity is not important, only their position.

Example: If type check produces a closure with the closure substs:

ClosureSubsts = [
    i8,                                  // the "closure kind"
    for<'x> fn(&'a &'x u32) -> &'x u32,  // the "closure signature"
    &'a String,                          // some upvar
]

here, there is one unique free region ('a) but it appears twice. We would "renumber" each occurence to a unique vid, as follows:

ClosureSubsts = [
    i8,                                  // the "closure kind"
    for<'x> fn(&'1 &'x u32) -> &'x u32,  // the "closure signature"
    &'2 String,                          // some upvar
]

Now the code might impose a requirement like '1: '2. When an instance of the closure is created, the corresponding free regions can be extracted from its type and constrained to have the given outlives relationship.

Fields

num_external_vids: usize

🔬 This is a nightly-only experimental API. (rustc_private)

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The number of external regions defined on the closure. In our example above, it would be 3 -- one for 'static, then '1 and '2. This is just used for a sanity check later on, to make sure that the number of regions we see at the callsite matches.

outlives_requirements: Vec<ClosureOutlivesRequirement>

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

Requirements between the various free regions defined in indices.

Trait Implementations

impl<'tcx> HashStable<StableHashingContext<'tcx>> for ClosureRegionRequirements

fn hash_stable<W: StableHasherResult>(
    &self,
    __ctx: &mut StableHashingContext<'tcx>,
    __hasher: &mut StableHasher<W>
)

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

impl Clone for ClosureRegionRequirements

fn clone(&self) -> ClosureRegionRequirements

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for ClosureRegionRequirements

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Encodable for ClosureRegionRequirements

fn encode<__S: Encoder>(&self, __arg_0: &mut __S) -> Result<(), __S::Error>

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?

impl Decodable for ClosureRegionRequirements

fn decode<__D: Decoder>(
    __arg_0: &mut __D
) -> Result<ClosureRegionRequirements, __D::Error>

🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?