• thebluepandabear (40/40) Jan 03 2023 I am using the CSFML D bindings, and I am creating my own `draw`
• =?UTF-8?Q?Ali_=c3=87ehreli?= (13/15) Jan 03 2023 It must be because T is already a type. It's the same reason why the
• thebluepandabear (3/18) Jan 03 2023 Ok, that makes sense now, my mistake. I seem to have gotten the

thebluepandabear <therealbluepandabear protonmail.com> writes:

I am using the CSFML D bindings, and I am creating my own `draw` 
template function.

I first check that the object passed in is of the appropriate 
type, and if it is, I call the appropriate function:

```D
template isDrawable(T) {
     enum isDrawable = is(T == sfCircleShape*) || is(T == 
sfRectangleShape*) || is(T == sfText*) || is(T == sfSprite*);
}

void sfRenderWindowExt_draw(T)(sfRenderWindow* renderWindow, T 
obj) {
     static assert(isDrawable!T, format("Cannot call any draw 
method on type %s", T.stringof));

     if (is(T == sfCircleShape*)) {
         
renderWindow.sfRenderWindow_drawCircleShape(cast(sfCircleShape*)obj, null);
     } else if (is(T == sfRectangleShape*)) {
         
renderWindow.sfRenderWindow_drawRectangleShape(cast(sfRectangleShape*)obj,
null);
     } else if (is(T == sfText*)) {
         renderWindow.sfRenderWindow_drawText(cast(sfText*)obj, 
null);
     } else if (is(T == sfSprite*)) {
         
renderWindow.sfRenderWindow_drawSprite(cast(sfSprite*)obj, null);
     }
}
```

For some reason, if I replace the `isDrawable` template with the 
following (using `typeof`), the code does not compile:

```D
template isDrawable(T) {
     enum isDrawable = is(typeof(T) == sfCircleShape*) || 
is(typeof(T) == sfRectangleShape*) || is(typeof(T) == sfText*) || 
is(typeof(T) == sfSprite*);
}
```

This is really strange, as I assumed that the two pieces of code 
were essentially the same.

Any help as to why this is the case would be appreciated.

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 1/3/23 20:11, thebluepandabear wrote:

 if I replace the `isDrawable` template with the
 following (using `typeof`), the code does not compile:

It must be because T is already a type. It's the same reason why the 
following code fails to compile:

void main() {
     alias T = int;
     alias TT = typeof(T);
}

Error: type `int` is not an expression

And the error message tells us typeof requires an expression. What you 
can do is to use T.init and the code should now work like the following 
does:

     alias TT = typeof(T.init);

Ali

thebluepandabear <therealbluepandabear protonmail.com> writes:

On Wednesday, 4 January 2023 at 04:42:08 UTC, Ali Çehreli wrote:
 On 1/3/23 20:11, thebluepandabear wrote:

 if I replace the `isDrawable` template with the
 following (using `typeof`), the code does not compile:

 It must be because T is already a type. It's the same reason 
 why the following code fails to compile:

 void main() {
     alias T = int;
     alias TT = typeof(T);
 }

 Error: type `int` is not an expression

 And the error message tells us typeof requires an expression. 
 What you can do is to use T.init and the code should now work 
 like the following does:

     alias TT = typeof(T.init);

 Ali

Ok, that makes sense now, my mistake. I seem to have gotten the 
wrong impression that typeof is more flexible than it is.