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?

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

I should have been more clear, but my actual question is how do I access the parameters of a template parameter.  My example works, but I wanted to know if there is a different and perhaps a better of doing it.

In your example it would look something like this:

struct SomeContainer(T, int x, int y){     }

struct Foo(alias ContainerType){

  // e.g.
  int my_x = ContainerType.x * 2;
  int my_y = ContainerType.y * 2;
}

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?

You later also said:

> how do I access the parameters of a template parameter

With the help of function template parameter deduction, I was able to do it by spelling out the parameters of Fun:

import std.stdio;

struct Box(T, int width, int height)
{
    void Fun(T2, int width2, int height2)(Box!(T2, width2, height2) b)
    {
        writeln(width2, ' ', height2);
    }
}

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

Ali