Re: why is this cast necessary?

[Steven Schveighoffer]

On Mon, 07 Jun 2010 23:02:48 -0400, Graham Fawcett <fawc...@uwindsor.ca>  
wrote:

Hi folks,
This program works as expected in D2:

    import std.stdio;
    import std.algorithm;

    T largestSubelement(T)(T[][] lol) {
      alias reduce!"a>b?a:b" max;
      return cast(T) max(map!max(lol));   // the cast matters...
    }

    void main() {
      auto a = [[1,2,3],[4,5,6],[8,9,7]];
      assert (largestSubelement(a) == 9);

      auto b = ["howdy", "pardner"];
      assert (largestSubelement(b) == 'y');

      auto c = [[1u, 3u, 45u, 2u], [29u, 1u]];
      assert (largestSubelement(c) == 45u);
    }

But if I leave out the 'cast(T)' in line 7, then this program will not
compile:

lse.d(6): Error: cannot implicitly convert expression
                  (reduce(map(lol))) of type dchar to immutable(char)
lse.d(14): Error: template instance
                   lse.largestSubelement!(immutable(char)) error
instantiating

Where did the 'dchar' came from? And why does the cast resolve the issue?

In a recent update, Andrei changed char[] and wchar[] to bi-directional  
ranges of dchar instead of straight arrays (at least, I think that was the  
change) in the eyes of the range types.  I think this is where the dchar  
comes from.

If you had a char[], and the 'max' element was a sequence of 2 code  
points, how do you return a single char for that result?

-Steve