• vit (33/33) May 06 2022 Hello, new dmd (2.100) has return/scope changes.
• Dennis (21/33) May 06 2022 `return scope` means pointer members (such `this.ptr`, `C.ptr`)
• vit (2/11) May 07 2022 Thanks

vit <vit vit.vit> writes:

Hello, new dmd (2.100) has return/scope changes.
It look like examples at page 
https://dlang.org/spec/function.html#ref-return-scope-parameters 
are no longer relevant.

What difference are between `return scope`, `scope return` and 
`return`?
Why `void* ptr` in struct change effect of `scope return` ?


```d
 safe:

struct A{
	int  val;
	//void* ptr;

	int* test() scope return{
		return &this.val;	// OK
	}
}

struct B{
	int  val;
	void* ptr;

	int* test() return{
		return &this.val; // OK
	}
}

struct C{
	int  val;
	void* ptr;

	int* test() scope return{
		return &this.val; // Error: returning `&this.val` escapes a 
reference to parameter `this`
	}
}


void main(){}
```

Dennis <dkorpel gmail.com> writes:

On Friday, 6 May 2022 at 09:24:06 UTC, vit wrote:
  It look like examples at page 
 https://dlang.org/spec/function.html#ref-return-scope-parameters are no longer
relevant.

They were recently updated to match the implementation in 2.100.

 What difference are between `return scope`, `scope return` and 
 `return`?

`return scope` means pointer members (such `this.ptr`, `C.ptr`) 
may not escape the function, unless they are returned. If you 
call `test()` on a `scope` variable, the return value will be a 
scope pointer.

`scope return` on a struct member is `scope` + `return ref`, 
meaning pointer members may not escape the function (the `scope` 
part), but you can return a reference to the struct member itself 
(`&this.val`, the `return ref` part). If you call `test()` on a 
local variable (`scope` or not), the return value will be a scope 
pointer.

Just `return` allows you to return a reference to the struct 
member itself (`&this.val`), and also to escape pointer members 
(`this.ptr`) since there is no `scope`. However, that means you 
can't call `test` on `scope` variables.

 ```
 	int* test() scope return{
 		return &this.val; // Error: returning `&this.val` escapes a 
 reference to parameter `this`
 	}
 }
 ```

I think you're using an older DMD version, the error should be 
gone in 2.100

 Why void* ptr in struct change effect of scope return ?

`scope` is ignored when the struct has no pointers, and before 
2.100, the meaning of `return` + `scope` on `ref` parameters was 
very inconsistent.

vit <vit vit.vit> writes:

On Friday, 6 May 2022 at 17:17:01 UTC, Dennis wrote:
 On Friday, 6 May 2022 at 09:24:06 UTC, vit wrote:
 [...]

 They were recently updated to match the implementation in 2.100.

 [...]

 `return scope` means pointer members (such `this.ptr`, `C.ptr`) 
 may not escape the function, unless they are returned. If you 
 call `test()` on a `scope` variable, the return value will be a 
 scope pointer.

 [...]

Thanks