Menu
Search

Forums

Forum Index

Thread overview
How do I call a context objects destructor or some type of exit() function automatically upon exiting a with {} scope?
April 01
Gravatar of Daniel Donnelly, Jr.Posted by Daniel Donnelly, Jr.Reply
Daniel Donnelly, Jr.
Gravatar of Daniel Donnelly, Jr.


Reply

I thought the destructor might automatically be called after with (new Context()) {} but it's not. Is there some sort of entry/exit functions like in Python?

April 01
Gravatar of Mike ParkerPosted by Mike Parker
in reply to Daniel Donnelly, Jr.		Reply
Mike Parker
Gravatar of Mike Parker
Posted in reply to Daniel Donnelly, Jr.


Reply

On Tuesday, 1 April 2025 at 16:54:50 UTC, Daniel Donnelly, Jr. wrote:

>

I thought the destructor might automatically be called after with (new Context()) {} but it's not. Is there some sort of entry/exit functions like in Python?

You've used new, which means it's allocated with the GC. In that case, your destructor is a finalizer and may or may not be called at any point during the program. It's non-deterministic.

If Context is a class, you can do this:

scope ctx = new Context;

This will allocate the class instance on the stack so the destructor will be called when the scope exits. And of course, if it's a struct, then just drop the new.

All of that said, D does have scope guards when you need them:

https://dlang.org/spec/statement.html#scope-guard-statement

April 01
Gravatar of Ali ÇehreliPosted by Ali Çehreli
in reply to Mike Parker		Reply
Ali Çehreli
Gravatar of Ali Çehreli
Posted in reply to Mike Parker


Reply
On 4/1/25 10:08 AM, Mike Parker wrote:
> ```
> scope ctx = new Context;
> ```
>
> This will allocate the class instance on the stack so the destructor
> will be called when the scope exits.

Another option is to call the destructor explicitly through destroy():

import std.stdio;

class C {
    ~this() {
        writeln("Goodbye");
    }
}

void foo() {
    auto c = new C();

    scope (exit) {
        destroy(c);    // <-- HERE
    }
}

void main() {
    writeln("Calling foo");
    foo();
    writeln("Exiting main");
}

Ali
April 01
Gravatar of Daniel Donnelly, Jr.Posted by Daniel Donnelly, Jr.
in reply to Mike Parker		Reply
Daniel Donnelly, Jr.
Gravatar of Daniel Donnelly, Jr.
Posted in reply to Mike Parker


Reply

On Tuesday, 1 April 2025 at 17:08:27 UTC, Mike Parker wrote:

>

On Tuesday, 1 April 2025 at 16:54:50 UTC, Daniel Donnelly, Jr. wrote:

>

[...]

You've used new, which means it's allocated with the GC. In that case, your destructor is a finalizer and may or may not be called at any point during the program. It's non-deterministic.

If Context is a class, you can do this:

scope ctx = new Context;

This will allocate the class instance on the stack so the destructor will be called when the scope exits. And of course, if it's a struct, then just drop the new.

All of that said, D does have scope guards when you need them:

https://dlang.org/spec/statement.html#scope-guard-statement

Thank you, that makes sense!

April 01
Gravatar of Daniel Donnelly, Jr.Posted by Daniel Donnelly, Jr.
in reply to Ali Çehreli		Reply
Daniel Donnelly, Jr.
Gravatar of Daniel Donnelly, Jr.
Posted in reply to Ali Çehreli


Reply
On Tuesday, 1 April 2025 at 17:33:02 UTC, Ali Çehreli wrote:
> On 4/1/25 10:08 AM, Mike Parker wrote:
> > ```
> > scope ctx = new Context;
> > ```
> >
> > This will allocate the class instance on the stack so the
> destructor
> > will be called when the scope exits.
>
> Another option is to call the destructor explicitly through destroy():
>
> import std.stdio;
>
> class C {
>     ~this() {
>         writeln("Goodbye");
>     }
> }
>
> void foo() {
>     auto c = new C();
>
>     scope (exit) {
>         destroy(c);    // <-- HERE
>     }
> }
>
> void main() {
>     writeln("Calling foo");
>     foo();
>     writeln("Exiting main");
> }
>
> Ali

Thanks! I will try this scope(exit) trick in order to pop the context internally, these contexts hold local variable definitions so of course I would want to pop them.