randomSample does not accept char[]

Timon Gehr timon.gehr at gmx.ch
Tue Jan 22 02:54:49 PST 2013


On 01/22/2013 11:42 AM, andrea9940 wrote:
> Hi everyone,
> can you explain me why this code DOES compile:
>
> /*-------------------------------------------------------*/
> import std.range, std.random;
> void main()
> {
>      int[] vowels = ['A', 'E', 'I', 'O', 'U'];
>      static assert(isInputRange!(typeof(vowels)));
>      auto x = randomSample(vowels, 1);
> }
> /*-------------------------------------------------------*/
>
> but this DOES NOT:
>
> /*-------------------------------------------------------*/
> import std.range, std.random;
> void main()
> {
>      char[] vowels = ['A', 'E', 'I', 'O', 'U'];
>      static assert(isInputRange!(typeof(vowels))); //pass
>      auto x = randomSample(vowels, 1); //fail
> }
> /*-------------------------------------------------------*/
> main.d(6): Error: template std.random.randomSample(R) if
> (isInputRange!(R)) does not match any function template declaration
> main.d(6): Error: template std.random.randomSample(R) if
> (isInputRange!(R)) cannot deduce template function from argument types
> !()(char[],int)

Use randomSample(vowels, 1, vowels.length); to make it work.

The error message is bad.
You are trying to call the following overload:

auto randomSample(R)(R r, size_t n)
     if(isInputRange!R && hasLength!R)
{
     return RandomSample!(R, void)(r, n, r.length);
}

hasLength!(char[]) is false. This is because Phobos considers char[], 
const(char)[] and immutable(char)[] ranges of dchar.




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