pub struct DebruijnIndex {
pub depth: u32,
}
🔬 This is a nightly-only experimental API. (rustc_private
)
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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)
^ ^ | | |
| | | | |
| +------------+ 1 | |
| | |
+--------------------------------+ 2 |
| |
+------------------------------------------+ 1
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 1, 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 2, 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 1, because the innermost binder in that location
is the outer fn.
🔬 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
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We maintain the invariant that this is never 0. So 1 indicates
the innermost binder. To ensure this, create with DebruijnIndex::new
.
🔬 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?
🔬 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?
🔬 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?
Performs copy-assignment from source
. Read more
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
Feeds this value into the given [Hasher
]. Read more
Feeds a slice of this type into the given [Hasher
]. Read more
🔬 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?
🔬 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?
Formats the value using the given formatter. Read more
This method returns an ordering between self
and other
values if one exists. Read more
This method tests less than (for self
and other
) and is used by the <
operator. Read more
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more
This method tests greater than (for self
and other
) and is used by the >
operator. Read more
This method tests greater than or equal to (for self
and other
) and is used by the >=
operator. Read more
This method returns an Ordering
between self
and other
. Read more
fn max(self, other: Self) -> Self | 1.21.0 [src] |
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self | 1.21.0 [src] |
Compares and returns the minimum of two values. Read more