}
}
-rustc_index::newtype_index! {
- /// A [De Bruijn index][dbi] 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 arrays
- /// 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.
- ///
- /// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
- #[derive(HashStable)]
- pub struct DebruijnIndex {
- DEBUG_FORMAT = "DebruijnIndex({})",
- const INNERMOST = 0,
- }
-}
-
pub type Region<'tcx> = &'tcx RegionKind;
/// Representation of regions. Note that the NLL checker uses a distinct
/// Region bound in a function scope, which will be substituted when the
/// function is called.
- ReLateBound(DebruijnIndex, BoundRegion),
+ ReLateBound(ty::DebruijnIndex, BoundRegion),
/// 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
}
}
-impl 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.
- #[must_use]
- pub fn shifted_in(self, amount: u32) -> DebruijnIndex {
- DebruijnIndex::from_u32(self.as_u32() + amount)
- }
-
- /// Update this index in place by shifting it "in" through
- /// `amount` number of binders.
- pub fn shift_in(&mut self, amount: u32) {
- *self = self.shifted_in(amount);
- }
-
- /// Returns the resulting index when this value is moved out from
- /// `amount` number of new binders.
- #[must_use]
- pub fn shifted_out(self, amount: u32) -> DebruijnIndex {
- DebruijnIndex::from_u32(self.as_u32() - amount)
- }
-
- /// Update in place by shifting out from `amount` binders.
- pub fn shift_out(&mut self, amount: u32) {
- *self = self.shifted_out(amount);
- }
-
- /// 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).
- pub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self {
- self.shifted_out(to_binder.as_u32() - INNERMOST.as_u32())
- }
-}
-
/// Region utilities
impl RegionKind {
/// Is this region named by the user?
}
}
- pub fn bound_at_or_above_binder(&self, index: DebruijnIndex) -> bool {
+ pub fn bound_at_or_above_binder(&self, index: ty::DebruijnIndex) -> bool {
match *self {
ty::ReLateBound(debruijn, _) => debruijn >= index,
_ => false,
projects / rust.git / blobdiff