On Sunday, 14 December 2025 at 12:32:23 UTC, yabobay wrote:
I have this piece of code:
```d
import std.stdio;
import std.container : SList;
import std.algorithm : each;
import std.range : retro;
void frob(const string s) {
SList!char ll;
s.retro.each!(c => ll.insertFront(c));
foreach (c; ll)
c.write;
writeln;
}
```
If i remove the call to `retro`, it compiles just fine. If i
change `each`'s operation to something like `writeln`, it
compiles just fine. But unchanged, this program will not
compile and will give this error:
```
test.d:8:12: error: none of the overloads of template
‘test.frob.each!((c) => ll.insertFront(c)).each’ are callable
using argument types ‘!()(Result!())’
8 | s.retro.each!(c => ll.insertFront(c));
| ^
/usr/lib/gcc/x86_64-pc-linux-gnu/15.2.1/include/d/std/algorithm/iteration.d:912:17:
note: Candidates are: ‘each(Range)(Range r)’
with `Range = Result!()`
must satisfy one of the following constraints:
` isRangeIterable!Range
__traits(compiles, typeof(r.front).length)`
912 | Flag!"each" each(Range)(Range r)
| ^
```
This is caused by [autodecoding][1], a feature of the standard
library where strings are automatically converted into Unicode
code points when used as ranges.
Because UTF-8 is a variable-length encoding, this means that when
a UTF-8 `string` is used as a range, it does not have a `.length`
property (read the linked article for a more thorough
explanation).
You can work around this using `std.utf.byCodeUnit` to treat the
string as a range of bytes instead of a range of code points:
```d
import std.utf : byCodeUnit;
s.byCodeUnit.retro.each!(...); // No error
```
[1]: https://jackstouffer.com/blog/d_auto_decoding_and_you.html
