cannot take address of scope local in safe function

[vit]

On Sunday, 13 June 2021 at 17:18:46 UTC, ag0aep6g wrote:
> On Sunday, 13 June 2021 at 16:27:18 UTC, vit wrote:
>> Why I can take address of Foo variable but not Bar?
>>
>> ```d
>> //-dip1000
>>
>> struct Foo{
>>     private double d;
>> }
>>
>> struct Bar{
>>     private void* ptr;
>> }
>>
>>
>>
>> void main()@safe{
>>     ///this is OK:
>>     {
>>         scope Foo x;
>>         scope ptr = &x;
>>     }
>>
>>     ///Error: cannot take address of `scope` local `x` in 
>> `@safe` function `main`:
>>     {
>>         scope Bar x;
>>         scope ptr = &x;
>>     }
>> }
>> ```
>
> `scope` affects indirections (i.e. pointers). `Foo` doesn't 
> contain any indirections, so `scope` doesn't mean anything for 
> it. The compiler just ignores it. It's like you wrote `Foo x;` 
> without `scope`.
>
> `Bar` does contain an indirection, so `scope` actually matters 
> and you get the error.

Thanks.

Is possible create and use scope output range allocated on stack 
in @safe code?

Example:
```d
//-dip1000

     struct OutputRange{
         private bool valid = true;
         private void* ptr;
     	int count = 0;

         void put(Val)(auto ref scope Val val){
             assert(this.valid == true);
         	this.count += 1;
         }


         ~this()scope pure nothrow @safe @nogc{
         	this.valid = false;
         }


     }

     void main()@safe pure nothrow @nogc{
         import std.algorithm : copy;
         import std.range : only;

         scope OutputRange or;

         only(1, 2, 3, 4).copy(&or);   ///Error: cannot take 
address of `scope` local `or` in `@safe` function `main`
         assert(or.count == 4);
     }

```