templateTest.d

void main(){
    import std.stdio;
    auto nodeI = new Node!(int)([1,2,3]);
    auto nodeF = new Node!(float)([1f,2f,3f]); /+ fails with error:
        $ dmd test.d
test.d(26): Error: function literal __lambda4 (int t) is not callable using argument types (float)
/Library/D/dmd/src/phobos/std/algorithm/iteration.d(480):        instantiated from here: MapResult!(__lambda1, float[])
test.d(26):        instantiated from here: map!(float[])
test.d(4):        instantiated from here: Node!(float, __lambda4)

       +/
       
    auto nodeF2 = new Node!(float, (float f) => f*f)([1f,2f,3f]); // works
    writeln(nodeI.test);
    writeln(nodeF.test);
}

template Node(T, alias func=(T t) => t*t){
    // Predefining the alias function seems to cause hassle with nodeF above
    class Node{
        T[] items;
        Node[] children;

        this(T[] ts){
            items = ts[];
        }

        static if(func is null){
            auto test(){
                return items;
            }
        }
        static if(func !is null){
            auto test(){
                import std.algorithm;
                return items.map!(a => func(a));
            }
        }
    }
}