Problems with OutputRanges

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I'm not sure what I'm doing wrong... the following code prints 
nothing:

void main()
{
     import std.stdio, std.range;
	
     string str = "asdf";
     auto sink = new dchar[](str.length);
     auto fun = (dchar c) { sink.put(c); };
     foreach (dchar c; str)
     {
         fun(c);
     }
     writeln(sink);
}

If I print sink's length inside the foreach loop, its length is 
reduced by 1 each step, until it's 0. That explains why nothing 
is being printed, but why is put altering the length of the array?