Struct rustc_type_ir::DebruijnIndex
source · pub struct DebruijnIndex {
pub(crate) private: u32,
}
Expand description
A De Bruijn index is a standard means of representing regions (and perhaps later types) in a higher-ranked setting. In particular, imagine a type like this:
for<'a> fn(for<'b> fn(&'b isize, &'a isize), &'a char)
// ^ ^ | | |
// | | | | |
// | +------------+ 0 | |
// | | |
// +----------------------------------+ 1 |
// | |
// +----------------------------------------------+ 0
In this type, there are two binders (the outer fn and the inner fn). We need to be able to determine, for any given region, which fn type it is bound by, the inner or the outer one. There are various ways you can do this, but a De Bruijn index is one of the more convenient and has some nice properties. The basic idea is to count the number of binders, inside out. Some examples should help clarify what I mean.
Let’s start with the reference type &'b isize
that is the first
argument to the inner function. This region 'b
is assigned a De
Bruijn index of 0, meaning “the innermost binder” (in this case, a
fn). The region 'a
that appears in the second argument type (&'a isize
) would then be assigned a De Bruijn index of 1, meaning “the
second-innermost binder”. (These indices are written on the arrows
in the diagram).
What is interesting is that De Bruijn index attached to a particular
variable will vary depending on where it appears. For example,
the final type &'a char
also refers to the region 'a
declared on
the outermost fn. But this time, this reference is not nested within
any other binders (i.e., it is not an argument to the inner fn, but
rather the outer one). Therefore, in this case, it is assigned a
De Bruijn index of 0, because the innermost binder in that location
is the outer fn.
Fields§
§private: u32
Implementations§
source§impl DebruijnIndex
impl DebruijnIndex
sourcepub const MAX_AS_U32: u32 = 4_294_967_040u32
pub const MAX_AS_U32: u32 = 4_294_967_040u32
Maximum value the index can take, as a u32
.
sourcepub const fn from_usize(value: usize) -> Self
pub const fn from_usize(value: usize) -> Self
sourcepub const unsafe fn from_u32_unchecked(value: u32) -> Self
pub const unsafe fn from_u32_unchecked(value: u32) -> Self
Creates a new index from a given u32
.
Safety
The provided value must be less than or equal to the maximum value for the newtype. Providing a value outside this range is undefined due to layout restrictions.
Prefer using from_u32
.
source§impl DebruijnIndex
impl DebruijnIndex
sourcepub fn shifted_in(self, amount: u32) -> DebruijnIndex
pub fn shifted_in(self, amount: u32) -> DebruijnIndex
Returns the resulting index when this value is moved into
amount
number of new binders. So, e.g., if you had
for<’a> fn(&’a x)
and you wanted to change it to
for<’a> fn(for<’b> fn(&’a x))
you would need to shift the index for 'a
into a new binder.
sourcepub fn shift_in(&mut self, amount: u32)
pub fn shift_in(&mut self, amount: u32)
Update this index in place by shifting it “in” through
amount
number of binders.
sourcepub fn shifted_out(self, amount: u32) -> DebruijnIndex
pub fn shifted_out(self, amount: u32) -> DebruijnIndex
Returns the resulting index when this value is moved out from
amount
number of new binders.
sourcepub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self
pub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self
Adjusts any De Bruijn indices so as to make to_binder
the
innermost binder. That is, if we have something bound at to_binder
,
it will now be bound at INNERMOST. This is an appropriate thing to do
when moving a region out from inside binders:
for<'a> fn(for<'b> for<'c> fn(&'a u32), _)
// Binder: D3 D2 D1 ^^
Here, the region 'a
would have the De Bruijn index D3,
because it is the bound 3 binders out. However, if we wanted
to refer to that region 'a
in the second argument (the _
),
those two binders would not be in scope. In that case, we
might invoke shift_out_to_binder(D3)
. This would adjust the
De Bruijn index of 'a
to D1 (the innermost binder).
If we invoke shift_out_to_binder
and the region is in fact
bound by one of the binders we are shifting out of, that is an
error (and should fail an assertion failure).
Trait Implementations§
source§impl Add<usize> for DebruijnIndex
impl Add<usize> for DebruijnIndex
source§impl Clone for DebruijnIndex
impl Clone for DebruijnIndex
source§fn clone(&self) -> DebruijnIndex
fn clone(&self) -> DebruijnIndex
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresource§impl Debug for DebruijnIndex
impl Debug for DebruijnIndex
source§impl From<DebruijnIndex> for u32
impl From<DebruijnIndex> for u32
source§fn from(v: DebruijnIndex) -> u32
fn from(v: DebruijnIndex) -> u32
source§impl From<DebruijnIndex> for usize
impl From<DebruijnIndex> for usize
source§fn from(v: DebruijnIndex) -> usize
fn from(v: DebruijnIndex) -> usize
source§impl From<u32> for DebruijnIndex
impl From<u32> for DebruijnIndex
source§impl From<usize> for DebruijnIndex
impl From<usize> for DebruijnIndex
source§impl Hash for DebruijnIndex
impl Hash for DebruijnIndex
source§impl<__CTX> HashStable<__CTX> for DebruijnIndexwhere
__CTX: HashStableContext,
impl<__CTX> HashStable<__CTX> for DebruijnIndexwhere __CTX: HashStableContext,
fn hash_stable(&self, __hcx: &mut __CTX, __hasher: &mut StableHasher)
source§impl Idx for DebruijnIndex
impl Idx for DebruijnIndex
source§impl Ord for DebruijnIndex
impl Ord for DebruijnIndex
source§fn cmp(&self, other: &DebruijnIndex) -> Ordering
fn cmp(&self, other: &DebruijnIndex) -> Ordering
1.21.0 · source§fn max(self, other: Self) -> Selfwhere
Self: Sized,
fn max(self, other: Self) -> Selfwhere Self: Sized,
source§impl PartialEq<DebruijnIndex> for DebruijnIndex
impl PartialEq<DebruijnIndex> for DebruijnIndex
source§fn eq(&self, other: &DebruijnIndex) -> bool
fn eq(&self, other: &DebruijnIndex) -> bool
self
and other
values to be equal, and is used
by ==
.source§impl PartialOrd<DebruijnIndex> for DebruijnIndex
impl PartialOrd<DebruijnIndex> for DebruijnIndex
source§fn partial_cmp(&self, other: &DebruijnIndex) -> Option<Ordering>
fn partial_cmp(&self, other: &DebruijnIndex) -> Option<Ordering>
1.0.0 · source§fn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
self
and other
) and is used by the <=
operator. Read moresource§impl Step for DebruijnIndex
impl Step for DebruijnIndex
source§fn steps_between(start: &Self, end: &Self) -> Option<usize>
fn steps_between(start: &Self, end: &Self) -> Option<usize>
step_trait
)source§fn forward_checked(start: Self, u: usize) -> Option<Self>
fn forward_checked(start: Self, u: usize) -> Option<Self>
step_trait
)source§fn backward_checked(start: Self, u: usize) -> Option<Self>
fn backward_checked(start: Self, u: usize) -> Option<Self>
step_trait
)source§fn forward(start: Self, count: usize) -> Self
fn forward(start: Self, count: usize) -> Self
step_trait
)source§unsafe fn forward_unchecked(start: Self, count: usize) -> Self
unsafe fn forward_unchecked(start: Self, count: usize) -> Self
step_trait
)source§fn backward(start: Self, count: usize) -> Self
fn backward(start: Self, count: usize) -> Self
step_trait
)source§unsafe fn backward_unchecked(start: Self, count: usize) -> Self
unsafe fn backward_unchecked(start: Self, count: usize) -> Self
step_trait
)source§impl<I: Interner> TypeFoldable<I> for DebruijnIndex
impl<I: Interner> TypeFoldable<I> for DebruijnIndex
source§fn try_fold_with<F: FallibleTypeFolder<I>>(
self,
_: &mut F
) -> Result<Self, F::Error>
fn try_fold_with<F: FallibleTypeFolder<I>>( self, _: &mut F ) -> Result<Self, F::Error>
source§fn fold_with<F: TypeFolder<I>>(self, _: &mut F) -> Self
fn fold_with<F: TypeFolder<I>>(self, _: &mut F) -> Self
try_fold_with
for use with infallible
folders. Do not override this method, to ensure coherence with
try_fold_with
.source§impl<I: Interner> TypeVisitable<I> for DebruijnIndex
impl<I: Interner> TypeVisitable<I> for DebruijnIndex
source§fn visit_with<F: TypeVisitor<I>>(&self, _: &mut F) -> ControlFlow<F::BreakTy>
fn visit_with<F: TypeVisitor<I>>(&self, _: &mut F) -> ControlFlow<F::BreakTy>
impl Copy for DebruijnIndex
impl Eq for DebruijnIndex
impl StructuralEq for DebruijnIndex
impl StructuralPartialEq for DebruijnIndex
impl TrustedStep for DebruijnIndex
Auto Trait Implementations§
impl RefUnwindSafe for DebruijnIndex
impl Send for DebruijnIndex
impl Sync for DebruijnIndex
impl Unpin for DebruijnIndex
impl UnwindSafe for DebruijnIndex
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T, R> CollectAndApply<T, R> for T
impl<T, R> CollectAndApply<T, R> for T
Layout§
Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...)
attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.
Size: 4 bytes