Passing functions as template parameter and assigning default values to them

[kerdemdemir via Digitalmars-d-learn]

Hi,

I need to find the index of maximum element so my code:

int indexOfMax(R)(R range)
{	
     alias Type = typeof(range.front().re);  ----> I don't like 
.re here
     Type max = 0;
     size_t maxIndex = 0;
     foreach ( index,elem; range )
     {
     	if ( elem.re > max )    -----> And also here
     	{
     	    max = elem.re;
     	    maxIndex = index;
     	}
     }
     return maxIndex;
}

Since my range contains Complex!double types I have to add ".re" 
for current implementation. But I want to be more generic. Like 
how std.algorithm.map is.
Like: range.map!(a => a.re).

So what I want to achive is :

indexOfMax!(a => a.re)(complexRange); ----> implement algorithm 
on a.re
indexOfMax(intRange); -----> if a function is not given act like 
(a => a)

Any advice with template function parameters or mixins will make 
me happy.

Regards
Erdem