Thread overview
How can I match every instance of a template type (struct)?
Jul 12
rempas
Jul 12
ag0aep6g
Jul 12
rempas
Jul 12
ag0aep6g
Jul 12
rempas
July 12

I want to do something like the following:

import core.stdc.stdio;

Test!(T, "mode1") make_test(T)(T data) {
  Test!(T, "mode1") t = { data };

  return t;
}

struct Test(T, string mode = "ref") { T data; }

extern (C) void main() {
  auto obj = make_test(20);
  static if (is(typeof(obj) == Test)) { printf("YES!!!!!!!\n"); }
}

So, I just want to be able check if a variable is a given struct type. I also want to be able to do something similar but having a (templated) function that returns a struct type without having to be limited to a specific initialization of it.

Obviously, the given code will not work. It will result to the following error message:

Error: template struct `test.Test(T, string mode = "ref")` is used as a type without instantiation; to instantiate it use `Test!(arguments)`

Any ideas? Also, like in every question I make, the solution must be "betterC" compatible.

CLARIFICATION
I have a bad feeling that the post is not clear enough, so I'll save us all some time by making it clear.
I know I can do this:

  static if (is(typeof(obj) == Test!(int, "mode1"))) { printf("YES!!!!!!!\n"); }

And it will work but this is not what I want. I want to much EVERY "Test" type regardless of what's the value
of its templated arguments.

July 12
On 12.07.22 15:34, rempas wrote:
> extern (C) void main() {
>    auto obj = make_test(20);
>    static if (is(typeof(obj) == Test)) { printf("YES!!!!!!!\n"); }
> }

static if (is(typeof(obj) == Test!T, T)) { printf("YES!!!!!!!\n"); }
July 12
On Tuesday, 12 July 2022 at 13:37:49 UTC, ag0aep6g wrote:
>
> static if (is(typeof(obj) == Test!T, T)) { printf("YES!!!!!!!\n"); }

Haaaaaah? Ok, what does this work anyway? I thought you needed parenthesis for more than 1 templated arguments...
July 12
On Tue, Jul 12, 2022 at 01:56:11PM +0000, rempas via Digitalmars-d-learn wrote:
> On Tuesday, 12 July 2022 at 13:37:49 UTC, ag0aep6g wrote:
> > 
> > static if (is(typeof(obj) == Test!T, T)) { printf("YES!!!!!!!\n"); }
> 
> Haaaaaah? Ok, what does this work anyway? I thought you needed parenthesis for more than 1 templated arguments...

If your template has multiple parameters, just write:

	static if (is(typeof(obj) == Test!Args, Args...)) ...


T

-- 
Don't drink and derive. Alcohol and algebra don't mix.
July 12

On Tuesday, 12 July 2022 at 13:56:11 UTC, rempas wrote:

>

On Tuesday, 12 July 2022 at 13:37:49 UTC, ag0aep6g wrote:

>

static if (is(typeof(obj) == Test!T, T)) { printf("YES!!!!!!!\n"); }

Haaaaaah? Ok, what does this work anyway? I thought you needed parenthesis for more than 1 templated arguments...

The second T is not a template argument. It's an operand of the "IsExpression".

You can read more about those expressions here:
https://dlang.org/spec/expression.html#is-parameter-list

July 12
On 7/12/22 06:34, rempas wrote:

>    static if (is(typeof(obj) == Test)) { printf("YES!!!!!!!\n"); }

An alternative:

  import std.traits;
  static if (isInstanceOf!(Test, typeof(obj))) { printf("YES!!!!!!!\n"); }

https://dlang.org/phobos/std_traits.html#isInstanceOf

Ali

July 12

On Tuesday, 12 July 2022 at 15:30:03 UTC, Ali Çehreli wrote:

>

An alternative:
https://dlang.org/phobos/std_traits.html#isInstanceOf

This is a really good alternative. Because I used to have to write longer. Thanks, the LOG thing is better now:

struct LOG(T...) {
  T[0] id;
  T[1] data;
}

void main()
{
   auto obj = //make_test(20);/*
              make_test('T');//*/

  alias typ = //typeof(obj);/*
        LOG!(int, char);//*/

  "Type: ".write;

  if(isInstanceOf!(LOG, typ)/*
    is(typ : Template!Args,
    alias Template, Args...)//*/
  ) "LOG".writeln;
}

SDB@79

July 12

On Tuesday, 12 July 2022 at 13:34:42 UTC, rempas wrote:

>

[...]

Thank you all for your help!

@Ali Çehreli

That makes things much much easier! I'll look at the source code in "traits.d" and I'll copy-paste it into my library ;)