toLower

[Nick Treleaven]

On Thursday, 17 August 2023 at 09:28:05 UTC, Joel wrote:
>             .map!(std.uni.toLower)
>             .sort!"a<b"
>             .writeln;
>     }
>     ```
>     onlineapp.d(8): Error: none of the overloads of template 
> `std.algorithm.sorting.sort` are callable using argument types 
> `!("a<b")(MapResult!(toLower, ByCodeUnitImpl))`
>     
> /dlang/dmd/linux/bin64/../../src/phobos/std/algorithm/sorting.d(1925):        Candidate is: `sort(alias less = "a < b", SwapStrategy ss = SwapStrategy.unstable, Range)(Range r)`
>       with `less = "a<b",
>            ss = SwapStrategy.unstable,
>            Range = MapResult!(toLower, ByCodeUnitImpl)`
>       must satisfy one of the following constraints:
>     `       hasSwappableElements!Range
>            hasAssignableElements!Range
>            ss != SwapStrategy.unstable`

`map` generates a range `r` whose elements can be accessed by 
mutable reference only if the result of calling the map function 
(on a source element) is a mutable reference. But 
`std.uni.toLower` returns by value, and `sort` requires `r.front` 
to be a mutable reference.

I'll look at improving the docs.