When I try to compile this code in Rust Playground using the default settings, I get the following error:

use std::collections::BTreeMap;
use std::ops::Bound::{Included, Excluded};

pub fn get_range(map: &BTreeMap<String, i32>, start: &str, end: &str) -> Vec<(String, i32)> {
    map
    .range((Included(start), Excluded(end)))
    .map(|(k, v)| (k.clone(), v.clone()))
    .collect()
}


pub fn main() {
    let map = BTreeMap::from_iter(vec![
        ("cherry".to_string(), 3),
        ("apple".to_string(), 1),
        ("banana".to_string(), 2),
    ]);

    let range = get_range(&map, "apple", "cherry");
    println!("Range [apple, cherry): {:?}", range);

}

Exited with status 101

Standard Error

   Compiling playground v0.0.1 (/playground)
error[E0283]: type annotations needed
    --> src/main.rs:6:6
     |
   6 |     .range((Included(start), Excluded(end)))
     |      ^^^^^ cannot infer type of the type parameter `T` declared on the method `range`
     |
     = note: cannot satisfy `_: Ord`
note: required by a bound in `BTreeMap::<K, V, A>::range`
    --> /playground/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/collections/btree/map.rs:1429:12
     |
1427 |     pub fn range<T: ?Sized, R>(&self, range: R) -> Range<'_, K, V>
     |            ----- required by a bound in this associated function
1428 |     where
1429 |         T: Ord,
     |            ^^^ required by this bound in `BTreeMap::<K, V, A>::range`
help: consider specifying the generic arguments
     |
   6 |     .range::<T, (Bound<&str>, Bound<&str>)>((Included(start), Excluded(end)))
     |           +++++++++++++++++++++++++++++++++

error[E0283]: type annotations needed
    --> src/main.rs:6:6
     |
   6 |     .range((Included(start), Excluded(end)))
     |      ^^^^^ cannot infer type of the type parameter `T` declared on the method `range`
     |
     = note: multiple `impl`s satisfying `String: Borrow<_>` found in the following crates: `alloc`, `core`:
             - impl Borrow<str> for String;
             - impl<T> Borrow<T> for T
               where T: ?Sized;
note: required by a bound in `BTreeMap::<K, V, A>::range`
    --> /playground/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/collections/btree/map.rs:1430:12
     |
1427 |     pub fn range<T: ?Sized, R>(&self, range: R) -> Range<'_, K, V>
     |            ----- required by a bound in this associated function
...
1430 |         K: Borrow<T> + Ord,
     |            ^^^^^^^^^ required by this bound in `BTreeMap::<K, V, A>::range`
help: consider specifying the generic arguments
     |
   6 |     .range::<T, (Bound<&str>, Bound<&str>)>((Included(start), Excluded(end)))
     |           +++++++++++++++++++++++++++++++++

For more information about this error, try `rustc --explain E0283`.
error: could not compile `playground` (bin "playground") due to 2 previous errors

When i modify the range call to this: range::<str, _>((Included(start), Excluded(end))). The code runs successfully.

Standard Output

Range [apple, cherry): [("apple", 1), ("banana", 2)]

I do not really understand the compiler reasoning. In my opinion, it should be clear from the trait bounds of the range method that the T parameter can only be a str in this case.

Am I missing something? Would the compiler see it differently? Could someone help me with this?

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