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digitalmars.D.learn - How can I match every instance of a template type (struct)?

reply rempas <rempas tutanota.com> writes:
I want to do something like the following:

```d
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:

```d
   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.
Jul 12 2022
next sibling parent reply ag0aep6g <anonymous example.com> writes:
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"); }
Jul 12 2022
parent reply rempas <rempas tutanota.com> writes:
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...
Jul 12 2022
next sibling parent "H. S. Teoh" <hsteoh qfbox.info> writes:
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.
Jul 12 2022
prev sibling parent ag0aep6g <anonymous example.com> writes:
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
Jul 12 2022
prev sibling next sibling parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
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
Jul 12 2022
parent Salih Dincer <salihdb hotmail.com> writes:
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:


```d
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
Jul 12 2022
prev sibling parent rempas <rempas tutanota.com> writes:
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 ;)
Jul 12 2022