On Sat, Jan 5, 2013 at 10:50 PM, ref2401 <refactor24@gmail.com> wrote:

I have a template function that must work with an array of float values.
something like this:

void foo(T : A[], A)(auto ref T arg)
if(is(A == float))
{
...
}

Array may be static or dynamic. But the length of the array must be 16 or 32. How can i test length value?

For a dynamic array, its type is T[] and the length is a known only at runtime (by definition). You can test it with a runtime test, but not with a template constraint.

For a static array T[n], n is part of the type so you can indeed filter the bad ones during compilation.

Using std.traits and std.range:

import std.array;

import std.traits;

import std.range;

void foo(T)(auto ref T arg)

if ( isDynamicArray!T && is(ElementType!T == float)

|| isStaticArray!T && (T.length == 16 || T.length == 32) && is(ElementType!T == float))

{}

void main()

{

float[] dynamicArr;

float[3] staticArr1 = [0.0,1.0,2.0];

float[16] staticArr2;

foo(dynamicArr);

//foo(staticArr1); // fails

foo(staticArr2);

}

Or, if you prefer using the is() expression:

void bar(T)(auto ref T arg)

if ( is(T _ == U[], U)

|| is(T _ == U[n], U, size_t n) && (n == 16 || n == 32))

{}

void main()

{

float[] dynamicArr;

float[3] staticArr1 = [0.0,1.0,2.0];

float[16] staticArr2;

bar(dynamicArr);

//bar(staticArr1); // fails

bar(staticArr2);

}