Re: template template parameter

[Ali Çehreli]

On 03/30/2011 04:32 PM, Caligo wrote:
I have a struct that looks something like this:
struct Box(T, size_t width, size_t height){

alias width width_;
alias height height_;

//do something with a Box of different size
   void Fun( B )(B b){
     // using width and height of b
     B.width_;
     B.height_;
   }
}

auto b1 = Box!(double, 2, 7)();
auto b2 = Box!(double, 3, 4)();
b1.Fun(b2);

I think the technical name for this is template template parameter.
Using the above I'm able to do what I need to do, but is there a
better way?
and should I use alias or enum?

Template template parameter means exactly that: a template parameter is 
itself a template. See ContainerType below:

struct SomeContainer(T)
{
    T[] elements;
}

struct SomeOtherContainer(T)
{
    struct List(T)
    {}

    // e.g. this one may use a linked list
    List!T elements;
}

struct Foo(alias ContainerType, T)
{
    // Instantiate the 'template template parameter'
    ContainerType!T member;
}

void main()
{
    Foo!(SomeContainer, double) foo1;
    Foo!(SomeOtherContainer, int) foo2;
}

ContainerType is a template parameter of Foo and is itself a template.

And 'alias' seems to work...

Ali