[Issue 21929] delegates capture do not respect scoping

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21929

--- Comment #13 from deadalnix <deadalnix at gmail.com> ---
(In reply to Walter Bright from comment #10)
> Replying to comment #1:
> 
> The observed behavior is a direct result of lambdas in D not capturing by
> value, they capture by reference.
> 

This is true of the first exemple, for which things behave apropriately.

This is not true of the second one, as, even though it capture by reference, it
capture a reference to a new variable every time.

> Even allocating a closure on the gc heap is not a solution here, because only one allocation will be made which will be shared by each lambda, exhibiting the same behavior.

What's nice when most options are incorrect, is that it's fairly obvious what
the correct ones are. in this cases, there are 3:
 - All variables have function scope, like in python.
 - A new closure is allocated for every loop iteration, like in JavaScript or
C#.
 - Don't pretend you are a safe language in any way like C++ and put the burden
of getting things right on the user.

Considering D as it stands, it is obvious that the second choice is the correct
one. But can also chose to do away with RAII and go for the first option. Or we
can get rid of @safe .

Or we can ignore the issue for one more decade and hope it goes away as
everybody moves to rust.

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