Re: Map one tuple to another Tuple of different type

[John Colvin via Digitalmars-d-learn]

On Monday, 21 July 2014 at 18:10:14 UTC, H. S. Teoh via 
Digitalmars-d-learn wrote:
On Mon, Jul 21, 2014 at 12:55:34AM +0200, Daniel Gibson via 
Digitalmars-d-learn wrote:
Hi,
I have a variadic templated function and want to call a C 
varargs function.
I want to be able to pass static arrays, which D2 passes by 
value and C by
reference, so I'd like to automagically translate those 
arguments.

My idea was something like this:

  extern (C) origFun(int x, ...);

  T transTupleElem(T)(T arg) { return arg; }

  float* transTupleElem(T : float[3])(T arg) {
    return arg.ptr;
  }

  void fun(T...)(int x, T argTuple) {
    // create a new tuple type that replaces all static 
float[3]
    // arrays with float* to emulate C call-by-reference 
behavior
    alias ReplaceAll!(float[3], float*, T) ModifiedTuple;
    ModifiedTuple modTuple;

    foreach(size_t i ; 0 .. T.length)
      modTuple[i] = transTupleElem(argTuple[i]); // BOOM!

    origFun(modTuple); // or is it modTuple.expand ?
  }

However, this doesn't work (dmd 2.065 linux64), because:
"Error: variable i cannot be read at compile time"
[...]

Try this:

        import std.typecons : staticIota;
        foreach (i; staticIota!(0, T.length))
                modTuple[i] = transTupleElem(argTuple[i]);


T

staticIota is marked package in std.typecons