Swap front for char[] input ranges

[Ali Çehreli via Digitalmars-d-learn]

On 12/19/2016 02:41 AM, RazvanN wrote:
 > Hi,
 >
 > I have a function which accepts 2 input Ranges

As your comments make it clear below, they cannot be InputRanges.

 > and swaps the first
 > element in Range1 with the first element in Range2. The swapping code
 > looks something like this :
 >
 >      static if (is(typeof(swap(r1.front, r2.front))))
 >      {
 >          swap(r1.front, r2.front);
 >      }
 >      else
 >      {
 >          auto t1 = moveFront(r1), t2 = moveFront(r2);
 >          auto tmp1 = r1.front;
 >          auto tmp2 = r2.front;

Obivously, tmp1 and tmp2 are unusued there. :)

 >          r1.front = move(t2);
 >          r2.front = move(t1);
 >      }
 >
 > This code works for most cases, except when 2 char[] are passed.
 > In that case, the compilation fails with error messages which state
 > that r1.front and r2.front are not Lvalues. So, my question is:
 > how can I swap the 2 elements since in the case of char[] input ranges
 > the front property does not return a reference?

Not possible... It's ok to use something similar to the following 
template constraint:

void foo(R1, R2)(R1 r1, R2 r2)
if ((hasSwappableElements!R1 && hasSwappableElements!R2) ||
     (hasLvalueElements!R1 && hasLvalueElements!R2)) {
     // ...
}

Ali