Re: Passing functions as template parameter and assigning default values to them

[biozic via Digitalmars-d-learn]

On Sunday, 21 June 2015 at 09:34:51 UTC, kerdemdemir wrote:
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

You can use a template alias parameter with a default value that 
is your default lambda:

int indexOfMax(alias fun = a => a, R)(R range)
{
    // Use `fun` here like a function.
}

-- Nico