• vit (16/16) Dec 28 2021 Hi, why this code doesn't compile?
• Tejas (23/39) Dec 28 2021 Since a destructor ignores `const`, I think adding the `~this` to
• vit (5/29) Dec 29 2021 Thanks, you are right, generated Bar.~this() try use opCast to

vit <vit vit.vit> writes:

Hi, why this code doesn't compile?

```d
struct Foo{
     bool opCast(T : bool)()const{
         assert(0);
     }

     ~this(){}
}

struct Bar{
     const Foo foo;
}

void main(){


}
```

Error: template instance `opCast!(Foo)` does not match template 
declaration `opCast(T : bool)()`

Tejas <notrealemail gmail.com> writes:

On Tuesday, 28 December 2021 at 18:27:36 UTC, vit wrote:
 Hi, why this code doesn't compile?

 ```d
 struct Foo{
     bool opCast(T : bool)()const{
         assert(0);
     }

     ~this(){}
 }

 struct Bar{
     const Foo foo;
 }

 void main(){


 }
 ```

 Error: template instance `opCast!(Foo)` does not match template 
 declaration `opCast(T : bool)()`

Since a destructor ignores `const`, I think adding the `~this` to 
Foo manually is somehow making the compiler have to actually cast 
away const, which it is doing via `cast(Foo) foo`, which fails 
since you've declared your own `opCast` that only accepts 
arguments implicitly convertible to `bool`.

I say this because removing the specialisation in `opCast` and 
changing the return type of it to `Foo` works :

```d
struct Foo{
     Foo opCast(T)()const {
         assert(0);
         return this;
     }
     ~this() {}

}

struct Bar{
     const Foo foo;

}

void main(){
     //Bar bar = Bar(); //this will trigger the assertion failure


}
```

vit <vit vit.vit> writes:

On Wednesday, 29 December 2021 at 01:00:53 UTC, Tejas wrote:
 On Tuesday, 28 December 2021 at 18:27:36 UTC, vit wrote:
 [...]

 Since a destructor ignores `const`, I think adding the `~this` 
 to Foo manually is somehow making the compiler have to actually 
 cast away const, which it is doing via `cast(Foo) foo`, which 
 fails since you've declared your own `opCast` that only accepts 
 arguments implicitly convertible to `bool`.

 I say this because removing the specialisation in `opCast` and 
 changing the return type of it to `Foo` works :

 ```d
 struct Foo{
     Foo opCast(T)()const {
         assert(0);
         return this;
     }
     ~this() {}

 }

 struct Bar{
     const Foo foo;

 }

 void main(){
     //Bar bar = Bar(); //this will trigger the assertion failure


 }
 ```

Thanks, you are right, generated Bar.~this() try use opCast to 
cast const away.
Is look like bug in compiler.

I stop using opCast for now.