On Friday, 9 November 2018 at 09:47:32 UTC, Vinay Sajip wrote:
std.utf.decodeFront(Flag useReplacementDchar =
No.useReplacementDchar, S)(ref S str) if (isInputRange!S &&
isSomeChar!(ElementType!S))
This is the overload you want, let's check if it matches:
ref S str - your InputRange can be passed by reference, but you
specified S = dchar. S here is the type of the inputRange, and it
is not of type dchar. It's best not to specify S so the compiler
will infer it, range types can be very complicated. Once we fix
that, let's look at the rest:
isInputRange!S - S is an inputRange
isSomeChar!(ElementType!S) - ElementType!S is ubyte, but
isSomeChar!ubyte is not true.
The function wants characters, but you give bytes. A quick fix
would be to do:
```
import std.algorithm: map;
auto mapped = r.map!(x => cast(char) x);
mapped.decodeFront!(No.useReplacementDchar)();
```
But it may be better for somefn to accept an InputRange!(char)
instead.
Note that if you directly do:
```
r.map!(x => cast(char) x).decodeFront!(No.useReplacementDchar)();
```
It still won't work, since it wants `ref S str` and r.map!(...)
is a temporary that can't be passed by reference.
As you can see, ensuring template constraints can be really
difficult. The error messages give little help here, so you have
to manually check whether the conditions of the overload you want
hold.
