RangeXxx<&T> should implement RangeBounds<T> even if T is unsized #107196
Description
I tried this code:
use std::collections::BTreeMap;
pub fn foo(map: &BTreeMap<String, i32>) -> impl Iterator<Item = (&String, &i32)> {
map.range::<str, _>("".."")
}I expected to see this happen: This should compile since BTreeMap::range is supposed to accept a RangeBounds with an unsized type parameter
Instead, this happened: It does not compile with the error:
error[[E0277]](https://doc.rust-lang.org/stable/error-index.html#E0277): the size for values of type `str` cannot be known at compilation time
--> src/lib.rs:3:25
|
3 | map.range::<str, _>("".."")
| ----- ^^^^^^ doesn't have a size known at compile-time
| |
| required by a bound introduced by this call
|
= help: the trait `Sized` is not implemented for `str`
= help: the following other types implement trait `RangeBounds<T>`:
std::ops::Range<&T>
std::ops::Range<T>
= note: required for `std::ops::Range<&str>` to implement `RangeBounds<str>`
note: required by a bound in `BTreeMap::<K, V, A>::range`
This is because Range<&str> does not implement RangeBounds<str>, because the current impl RangeBounds<str> for Range<&str> is as follows:
#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for Range<&T> {
fn start_bound(&self) -> Bound<&T> {
Included(self.start)
}
fn end_bound(&self) -> Bound<&T> {
Excluded(self.end)
}
}Similarly, for other range structs except (Bound, Bound) and RangeFull (the latter of which does not have a type anyway), the type parameter is unnecessarily constrained to be sized:
The implicit Sized bound on T for the RangeXxx<&T> cases appears to be unintentional judging from the fact that there are no comments explaining this decision.
Meta
rustc --version --verbose:
rustc 1.66.1 (90743e729 2023-01-10)
binary: rustc
commit-hash: 90743e7298aca107ddaa0c202a4d3604e29bfeb6
commit-date: 2023-01-10
host: x86_64-unknown-linux-gnu
release: 1.66.1
LLVM version: 15.0.2
Backtrace
<backtrace>