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digitalmars.D.learn - Multiple destructors

reply Alex Biscotti <skyswood gmail.com> writes:
Hello everyone! While researching the phobos library, I 
discovered that a class can have multiple destructors if the 
destructors are added via mixin injection. Accordingly, the 
question is whether a description of such feature should be added 
to the documentation, since the current description is a bit 
confusing - ["There can be only one destructor per 
class"](https://dlang.org/spec/class.html#destructors)?

Here's a code demo of what I'm talking about:
```d
import std;

mixin template AddNewDtor()
{
     ~this()
     {
         writeln("Mixin dtor");
     }
}

class Foo
{
     ~this()
     {
         writeln("Class dtor");
     }

     mixin AddNewDtor;
}

void main()
{
     {
         auto s = scoped!Foo;

     	// prints `Mixin dtor`
         // prints `Class dtor`
     }
}
```
May 26 2023
next sibling parent reply Ernesto Castellotti <erny.castell gmail.com> writes:
On Friday, 26 May 2023 at 09:07:07 UTC, Alex Biscotti wrote:
 Hello everyone! While researching the phobos library, I 
 discovered that a class can have multiple destructors if the 
 destructors are added via mixin injection. Accordingly, the 
 question is whether a description of such feature should be 
 added to the documentation, since the current description is a 
 bit confusing - ["There can be only one destructor per 
 class"](https://dlang.org/spec/class.html#destructors)?

 [...]
This is a bug to me, you should open an issue on bugzilla
May 26 2023
parent reply Alex Biscotti <skyswood gmail.com> writes:
On Friday, 26 May 2023 at 09:11:47 UTC, Ernesto Castellotti wrote:
 On Friday, 26 May 2023 at 09:07:07 UTC, Alex Biscotti wrote:
 Hello everyone! While researching the phobos library, I 
 discovered that a class can have multiple destructors if the 
 destructors are added via mixin injection. Accordingly, the 
 question is whether a description of such feature should be 
 added to the documentation, since the current description is a 
 bit confusing - ["There can be only one destructor per 
 class"](https://dlang.org/spec/class.html#destructors)?

 [...]
This is a bug to me, you should open an issue on bugzilla
Do you mean that it's a bug in the documentation or implementation of the language?
May 26 2023
parent reply Ernesto Castellotti <erny.castell gmail.com> writes:
On Friday, 26 May 2023 at 09:17:34 UTC, Alex Biscotti wrote:
 On Friday, 26 May 2023 at 09:11:47 UTC, Ernesto Castellotti 
 wrote:
 On Friday, 26 May 2023 at 09:07:07 UTC, Alex Biscotti wrote:
 Hello everyone! While researching the phobos library, I 
 discovered that a class can have multiple destructors if the 
 destructors are added via mixin injection. Accordingly, the 
 question is whether a description of such feature should be 
 added to the documentation, since the current description is 
 a bit confusing - ["There can be only one destructor per 
 class"](https://dlang.org/spec/class.html#destructors)?

 [...]
This is a bug to me, you should open an issue on bugzilla
Do you mean that it's a bug in the documentation or implementation of the language?
Bug in the implementation of Mixin Template
May 26 2023
parent reply Alex Biscotti <skyswood gmail.com> writes:
On Friday, 26 May 2023 at 09:24:29 UTC, Ernesto Castellotti wrote:
 On Friday, 26 May 2023 at 09:17:34 UTC, Alex Biscotti wrote:
 On Friday, 26 May 2023 at 09:11:47 UTC, Ernesto Castellotti 
 wrote:
 On Friday, 26 May 2023 at 09:07:07 UTC, Alex Biscotti wrote:
 Hello everyone! While researching the phobos library, I 
 discovered that a class can have multiple destructors if the 
 destructors are added via mixin injection. Accordingly, the 
 question is whether a description of such feature should be 
 added to the documentation, since the current description is 
 a bit confusing - ["There can be only one destructor per 
 class"](https://dlang.org/spec/class.html#destructors)?

 [...]
This is a bug to me, you should open an issue on bugzilla
Do you mean that it's a bug in the documentation or implementation of the language?
Bug in the implementation of Mixin Template
Hmm, this feature is used in Phobos in [std.signal](https://github.com/dlang/phobos/blob/master/std/signals.d#L259). Actually, this is how I found it, since I implemented the Signal functionality, but without garbage collection. It seems to me that this is an undocumented feature, rather than a bug.
May 26 2023
parent reply Ernesto Castellotti <erny.castell gmail.com> writes:
On Friday, 26 May 2023 at 09:39:29 UTC, Alex Biscotti wrote:
 On Friday, 26 May 2023 at 09:24:29 UTC, Ernesto Castellotti 
 wrote:
 On Friday, 26 May 2023 at 09:17:34 UTC, Alex Biscotti wrote:
 On Friday, 26 May 2023 at 09:11:47 UTC, Ernesto Castellotti 
 wrote:
 On Friday, 26 May 2023 at 09:07:07 UTC, Alex Biscotti wrote:
 Hello everyone! While researching the phobos library, I 
 discovered that a class can have multiple destructors if 
 the destructors are added via mixin injection. Accordingly, 
 the question is whether a description of such feature 
 should be added to the documentation, since the current 
 description is a bit confusing - ["There can be only one 
 destructor per 
 class"](https://dlang.org/spec/class.html#destructors)?

 [...]
This is a bug to me, you should open an issue on bugzilla
Do you mean that it's a bug in the documentation or implementation of the language?
Bug in the implementation of Mixin Template
Hmm, this feature is used in Phobos in [std.signal](https://github.com/dlang/phobos/blob/master/std/signals.d#L259). Actually, this is how I found it, since I implemented the Signal functionality, but without garbage collection. It seems to me that this is an undocumented feature, rather than a bug.
Currently the spec says "If the name of a declaration in a mixin is the same as a declaration in the surrounding scope, the surrounding declaration overrides the mixin one", I understand why this occurs with the current implementation, but either way the implementation should be changed or the specs should be clarified to explain this specific behavior with destructors.
May 26 2023
parent Alex Biscotti <skyswood gmail.com> writes:
On Friday, 26 May 2023 at 09:49:21 UTC, Ernesto Castellotti wrote:
 Currently the spec says "If the name of a declaration in a 
 mixin is the same as a declaration in the surrounding scope, 
 the surrounding declaration overrides the mixin one", I 
 understand why this occurs with the current implementation, but 
 either way the implementation should be changed or the specs 
 should be clarified to explain this specific behavior with 
 destructors.
Thank you for the clarification. I'll try to open an issue on bugzilla.
May 26 2023
prev sibling parent Basile B. <b2.temp gmx.com> writes:
On Friday, 26 May 2023 at 09:07:07 UTC, Alex Biscotti wrote:
 Hello everyone! While researching the phobos library, I 
 discovered that a class can have multiple destructors if the 
 destructors are added via mixin injection. Accordingly, the 
 question is whether a description of such feature should be 
 added to the documentation, since the current description is a 
 bit confusing - ["There can be only one destructor per 
 class"](https://dlang.org/spec/class.html#destructors)?
This is not a compiler bug, mixin templates are allowed to introduce a dtor; observe the output of ```d import std; mixin template AddNewDtor() { ~this() { writeln("Mixin dtor"); } } class Foo { ~this() { writeln("Class dtor"); } mixin AddNewDtor; } void main() { { Foo s = new Foo; writeln("-- dtor effect --"); s.__dtor; } { Foo s = new Foo; writeln("-- xdtor effect --"); s.__xdtor; } writeln("-- auto generated destruction... --"); } ``` as you can see, the internal `__xdtor` function is designed to call the two destructors, while `__dtor` only the "normal one", i.e the one that 's not mixed in. This is more a documentation bug IMO.
May 26 2023