Use of templates to avoid redudancy of code

[Lutger]

Mael wrote:

> Hello,
> 
> I'm writing an algorithm that has, say, too possible behaviour depending
> on a switch. Since there are many imbricated loops, and the behaviour
> change is inside the loop, testing for the flag is time-consuming
> 
> for( ....)
> for( .... )
> for( ... )
> {
>   if( flag ) action_1 ;
>   else action_2 ;
> }
> 
> is there a clean way to use templates to generate the duplicate of the
> code like
> 
> if( flag )
> {
>   for(...) .... action1 ;
> }
> else
> {
>   for(...) .... action2 ;
> }

If flag is a compile time constant, then you don't need no templates, just
this:

static if (flag) action_1
else action_2

The if is evaluated only at compile time.

If behavior is changed at runtime, it would depend a little on the rest of
the code, there are some different ways to implement if. For example as a
helper function:

void func(bool flag)
{
    if (flag)
        helper!(true)();
    else 
        helper!(false)();       
}

void helper(bool flag)()
{
    for( ....)
    for( .... )
    for( ... )
    {
       static if( flag ) action_1 ;
       else action_2 ;
    }
}