Hi all,
  What am I doing wrong here?
```
import std.algorithm;
int foo(char c) {
    return 123;
}
auto mapFoo(char[] chars) {
    return chars.map!(a => a.foo);
}
```
errors with:
main.d(14): Error: function main.foo (char c) is not callable using argument types (dchar)
/Library/D/dmd/src/phobos/std/algorithm/iteration.d(492):        instantiated from here: MapResult!(__lambda2, char[])
main.d(14):        instantiated from here: map!(char[])

(Things work after changing foo to accept dchar, but I don't want that.)

Thanks,
  Johan

On Monday, 24 July 2017 at 09:05:43 UTC, Johan wrote:
> Hi all,
>   What am I doing wrong here?
> ```
> import std.algorithm;
> int foo(char c) {
>     return 123;
> }
> auto mapFoo(char[] chars) {
>     return chars.map!(a => a.foo);
> }
> ```
> errors with:
> main.d(14): Error: function main.foo (char c) is not callable using argument types (dchar)
> /Library/D/dmd/src/phobos/std/algorithm/iteration.d(492):
>  instantiated from here: MapResult!(__lambda2, char[])
> main.d(14):        instantiated from here: map!(char[])
>
> (Things work after changing foo to accept dchar, but I don't want that.)
>
> Thanks,
>   Johan

Have a look at https://tour.dlang.org/tour/en/gems/unicode

tl;dr: it's auto-decoding and you can avoid it with e.g. byChar

It is worth noting too that mach's map function will not behave this way; UTF encoding and decoding is instructed explicitly and is not done implicitly like in phobos.

https://github.com/pineapplemachine/mach.d

    import mach.range : map, asarray;
    import mach.text.ascii : toupper;

    void main(){
        char[] x = ['h', 'e', 'l', 'l', 'o'];
        char[] y = x.map!toupper.asarray();
        assert(y == "HELLO");
    }