July 24, 2011
I needed a small script for a project of mine and hacked one in python. Since I want to learn some D, I tried to convert it. Took me a bit longer than I thought, because I got delayed by this lovely error message:

Error: template instance ambiguous template declaration
std.array.replace(R1,R2,R3) if (isDynamicArray!(R1) && isForwardRange!(R2)
&& isForwardRange!(R3) && (hasLength!(R3) || isSomeString!(R3))) and
std.regex.replace(Range,Engine,String) if (is(Unqual!(Engine) == Regex!
(Unqual!(typeof(Range.init[0])))))

Took me a while do understand it, but it seems that I've got a name collision. What I don't understand is, why is the compiler unable to tell two functions, one with two parameter and one with three, apart?


July 24, 2011
On 24.07.2011 20:46, Tobias Pankrath wrote:
> I needed a small script for a project of mine and hacked one in python.
> Since I want to learn some D, I tried to convert it. Took me a bit longer
> than I thought, because I got delayed by this lovely error message:
>
> Error: template instance ambiguous template declaration
> std.array.replace(R1,R2,R3) if (isDynamicArray!(R1)&&  isForwardRange!(R2)
> &&  isForwardRange!(R3)&&  (hasLength!(R3) || isSomeString!(R3))) and
> std.regex.replace(Range,Engine,String) if (is(Unqual!(Engine) == Regex!
> (Unqual!(typeof(Range.init[0])))))
>
> Took me a while do understand it, but it seems that I've got a name
> collision. What I don't understand is, why is the compiler unable to
> tell two functions, one with two parameter and one with three, apart?
>
Apparently, this overload of replace has 3 parameters: input, what to replace  and a replacement. It searches and replaces all occurrences.

I've hit the same issue while implementing a replacement for std.regex, the underlying problem I think is that
std.array.replace has a way too lousy template constraint. According to source it checks only if it's input is a range or string,  but if it has compatible type is *not* checked.

Now with std.regex since RegexMatch is ForwardRange it's of course matches, but element type is string/wstring/dstring, while I suppose std.array in this case would need element type of dchar.

It hadn't occurred to me that somebody will hit this anytime soon, so now I might roll out a pull request sooner :)

-- 
Dmitry Olshansky

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