Enum rustc::ty::RegionKind

pub enum RegionKind {
    ReEarlyBound(EarlyBoundRegion),
    ReLateBound(DebruijnIndex, BoundRegion),
    ReFree(FreeRegion),
    ReScope(Scope),
    ReStatic,
    ReVar(RegionVid),
    ReSkolemized(SkolemizedRegionVid, BoundRegion),
    ReEmpty,
    ReErased,
}

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Representation of regions.

Unlike types, most region variants are "fictitious", not concrete, regions. Among these, ReStatic, ReEmpty and ReScope are the only ones representing concrete regions.

Bound Regions

These are regions that are stored behind a binder and must be substituted with some concrete region before being used. There are 2 kind of bound regions: early-bound, which are bound in an item's Generics, and are substituted by a Substs, and late-bound, which are part of higher-ranked types (e.g. for<'a> fn(&'a ())) and are substituted by the likes of liberate_late_bound_regions. The distinction exists because higher-ranked lifetimes aren't supported in all places. See [1][2].

Unlike TyParam-s, bound regions are not supposed to exist "in the wild" outside their binder, e.g. in types passed to type inference, and should first be substituted (by skolemized regions, free regions, or region variables).

Skolemized and Free Regions

One often wants to work with bound regions without knowing their precise identity. For example, when checking a function, the lifetime of a borrow can end up being assigned to some region parameter. In these cases, it must be ensured that bounds on the region can't be accidentally assumed without being checked.

The process of doing that is called "skolemization". The bound regions are replaced by skolemized markers, which don't satisfy any relation not explicitly provided.

There are 2 kinds of skolemized regions in rustc: ReFree and ReSkolemized. When checking an item's body, ReFree is supposed to be used. These also support explicit bounds: both the internally-stored scope, which the region is assumed to outlive, as well as other relations stored in the FreeRegionMap. Note that these relations aren't checked when you make_subregion (or eq_types), only by resolve_regions_and_report_errors.

When working with higher-ranked types, some region relations aren't yet known, so you can't just call resolve_regions_and_report_errors. ReSkolemized is designed for this purpose. In these contexts, there's also the risk that some inference variable laying around will get unified with your skolemized region: if you want to check whether for<'a> Foo<'_>: 'a, and you substitute your bound region 'a with a skolemized region '%a, the variable '_ would just be instantiated to the skolemized region '%a, which is wrong because the inference variable is supposed to satisfy the relation for every value of the skolemized region. To ensure that doesn't happen, you can use leak_check. This is more clearly explained by infer/higher_ranked/README.md.

[1] http://smallcultfollowing.com/babysteps/blog/2013/10/29/intermingled-parameter-lists/ [2] http://smallcultfollowing.com/babysteps/blog/2013/11/04/intermingled-parameter-lists/

Variants

ReEarlyBound(EarlyBoundRegion)

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ReLateBound(DebruijnIndex, BoundRegion)

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ReFree(FreeRegion)

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When checking a function body, the types of all arguments and so forth that refer to bound region parameters are modified to refer to free region parameters.

ReScope(Scope)

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A concrete region naming some statically determined scope (e.g. an expression or sequence of statements) within the current function.

ReStatic

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Static data that has an "infinite" lifetime. Top in the region lattice.

ReVar(RegionVid)

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A region variable. Should not exist after typeck.

ReSkolemized(SkolemizedRegionVid, BoundRegion)

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A skolemized region - basically the higher-ranked version of ReFree. Should not exist after typeck.

ReEmpty

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Empty lifetime is for data that is never accessed. Bottom in the region lattice. We treat ReEmpty somewhat specially; at least right now, we do not generate instances of it during the GLB computations, but rather generate an error instead. This is to improve error messages. The only way to get an instance of ReEmpty is to have a region variable with no constraints.

ReErased

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Erased region, used by trait selection, in MIR and during trans.

Methods

impl RegionKind

Region utilities

pub fn is_late_bound(&self) -> bool

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pub fn needs_infer(&self) -> bool

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pub fn escapes_depth(&self, depth: u32) -> bool

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pub fn from_depth(&self, depth: u32) -> RegionKind

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Returns the depth of self from the (1-based) binding level depth

pub fn type_flags(&self) -> TypeFlags

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pub fn free_region_binding_scope(&self, tcx: TyCtxt) -> DefId

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Given an early-bound or free region, returns the def-id where it was bound. For example, consider the regions in this snippet of code:

impl<'a> Foo {
     ^^ -- early bound, declared on an impl

    fn bar<'b, 'c>(x: &self, y: &'b u32, z: &'c u64) where 'static: 'c
           ^^  ^^     ^ anonymous, late-bound
           |   early-bound, appears in where-clauses
           late-bound, appears only in fn args
    {..}
}

Here, free_region_binding_scope('a) would return the def-id of the impl, and for all the other highlighted regions, it would return the def-id of the function. In other cases (not shown), this function might return the def-id of a closure.

Trait Implementations

impl<'gcx> HashStable<StableHashingContext<'gcx>> for RegionKind

fn hash_stable<W: StableHasherResult>(
    &self,
    hcx: &mut StableHashingContext<'gcx>,
    hasher: &mut StableHasher<W>
)

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impl Clone for RegionKind

fn clone(&self) -> RegionKind

Returns a copy of the value.

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

Performs copy-assignment from source.

impl PartialEq for RegionKind

fn eq(&self, __arg_0: &RegionKind) -> bool

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

fn ne(&self, __arg_0: &RegionKind) -> bool

This method tests for !=.

impl Eq for RegionKind

impl Hash for RegionKind

fn hash<__H: Hasher>(&self, __arg_0: &mut __H)

Feeds this value into the given [Hasher].

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

Feeds a slice of this type into the given [Hasher].

impl Copy for RegionKind

impl Encodable for RegionKind

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

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impl Decodable for RegionKind

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

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impl PartialOrd for RegionKind

fn partial_cmp(&self, __arg_0: &RegionKind) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, __arg_0: &RegionKind) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, __arg_0: &RegionKind) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, __arg_0: &RegionKind) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, __arg_0: &RegionKind) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Ord for RegionKind

fn cmp(&self, __arg_0: &RegionKind) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

impl Print for RegionKind

fn print<F: Write>(&self, f: &mut F, cx: &mut PrintContext) -> Result

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fn print_to_string(&self, cx: &mut PrintContext) -> String

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fn print_display<F: Write>(&self, f: &mut F, cx: &mut PrintContext) -> Result

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fn print_display_to_string(&self, cx: &mut PrintContext) -> String

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fn print_debug<F: Write>(&self, f: &mut F, cx: &mut PrintContext) -> Result

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fn print_debug_to_string(&self, cx: &mut PrintContext) -> String

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impl Display for RegionKind

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

Formats the value using the given formatter.

impl Debug for RegionKind

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

Formats the value using the given formatter.