• rempas (21/21) Jun 18 2023 Ok, so I'm having a struct that has a constructor that takes a
• Paul Backus (10/31) Jun 18 2023 `__ctor` doesn't create a new object, it initializes an existing
• rempas (6/15) Jun 18 2023 Thank you! Do you know any other way to do it without using
• Paul Backus (18/32) Jun 18 2023 No, there is no way to pass template arguments to a constructor
• rempas (3/20) Jun 18 2023 Thank you! This will make me change the design of my API a little

rempas <rempas tutanota.com> writes:

Ok, so I'm having a struct that has a constructor that takes a 
template parameter. I suppose this question could also be named 
`how to initialize constructors with template parameters` but 
whatever! The funny thing is, I think that I may have already 
found how to do it in the past but I forgot... This time, I'm 
going to add the code in a big module in my project so I'm not 
going to have it as a reference and I won't forget it.

Here is a small sample code:

```d
import std.stdio;

struct Test {
   this(string type = "def")(string reg_arg) {
     writeln("reg_arg: ", reg_arg);
   }
}

void main() {
   auto test = Test.__ctor!("non_def")("Hello");
}
```

And the error I get: `test.d(10): Error: need `this` for `this` 
of type `ref  safe Test(string reg_arg)`

Paul Backus <snarwin gmail.com> writes:

On Sunday, 18 June 2023 at 17:43:01 UTC, rempas wrote:
 Ok, so I'm having a struct that has a constructor that takes a 
 template parameter. I suppose this question could also be named 
 `how to initialize constructors with template parameters` but 
 whatever! The funny thing is, I think that I may have already 
 found how to do it in the past but I forgot... This time, I'm 
 going to add the code in a big module in my project so I'm not 
 going to have it as a reference and I won't forget it.

 Here is a small sample code:

 ```d
 import std.stdio;

 struct Test {
   this(string type = "def")(string reg_arg) {
     writeln("reg_arg: ", reg_arg);
   }
 }

 void main() {
   auto test = Test.__ctor!("non_def")("Hello");
 }
 ```

 And the error I get: `test.d(10): Error: need `this` for `this` 
 of type `ref  safe Test(string reg_arg)`

`__ctor` doesn't create a new object, it initializes an existing 
object. You need to create the object first, then call `__ctor` 
on it:

```d
void main() {
   Test test;
   test.__ctor!("non_def")("Hello");
}
```

rempas <rempas tutanota.com> writes:

On Sunday, 18 June 2023 at 18:17:16 UTC, Paul Backus wrote:
 `__ctor` doesn't create a new object, it initializes an 
 existing object. You need to create the object first, then call 
 `__ctor` on it:

 ```d
 void main() {
   Test test;
   test.__ctor!("non_def")("Hello");
 }
 ```

Thank you! Do you know any other way to do it without using 
"__ctor".

I'm not sure if it was clear that it's not that I specifically 
want to do it with "__ctor" so I'm making it clear just to be 
sure.

Paul Backus <snarwin gmail.com> writes:

On Sunday, 18 June 2023 at 19:05:19 UTC, rempas wrote:
 On Sunday, 18 June 2023 at 18:17:16 UTC, Paul Backus wrote:
 `__ctor` doesn't create a new object, it initializes an 
 existing object. You need to create the object first, then 
 call `__ctor` on it:

 ```d
 void main() {
   Test test;
   test.__ctor!("non_def")("Hello");
 }
 ```

 Thank you! Do you know any other way to do it without using 
 "__ctor".

No, there is no way to pass template arguments to a constructor 
without using `__ctor`.

My recommendation is to use a free function or a `static` method 
instead. For example:

```d
import std.stdio;

struct Test {}

Test makeTest(string type = "def")(string reg_arg)
{
     writeln("reg_arg: ", reg_arg);
     return Test();
}

void main()
{
     auto test = makeTest!"non_def"("Hello");
}
```

rempas <rempas tutanota.com> writes:

On Sunday, 18 June 2023 at 19:22:45 UTC, Paul Backus wrote:
 No, there is no way to pass template arguments to a constructor 
 without using `__ctor`.

 My recommendation is to use a free function or a `static` 
 method instead. For example:

 ```d
 import std.stdio;

 struct Test {}

 Test makeTest(string type = "def")(string reg_arg)
 {
     writeln("reg_arg: ", reg_arg);
     return Test();
 }

 void main()
 {
     auto test = makeTest!"non_def"("Hello");
 }
 ```

Thank you! This will make me change the design of my API a little 
bit but it will do ;)