• Russ (24/24) Feb 22 2020 Hi, I've been playing around with having classes allocated on the
• Steven Schveighoffer (10/11) Feb 22 2020 scope escapes are only disallowed in @safe code.
• Russ (4/16) Feb 22 2020 Perfect, thank you! I agree that this sort of thing should be on

Russ <russpowers gmail.com> writes:

Hi, I've been playing around with having classes allocated on the 
stack. I am using the scope keyword for local variables. I 
assumed that the scope modifier for function parameters was 
designed to prevent these from escaping, but the code below 
doesn't show any errors. Is there some newer feature I should be 
using? Thanks.

import std.stdio;

class Foo
{
}

class Bar
{
	Foo foo;
}

void doSomething(scope Foo z, Bar b)
{
	b.foo = z;
}

void main()
{
	Bar b = new Bar;
	scope foo = new Foo;
	doSomething(foo, b);
}

Steven Schveighoffer <schveiguy gmail.com> writes:

On 2/22/20 10:01 PM, Russ wrote:
 Is there some newer feature I should be using?

scope escapes are only disallowed in  safe code.

Adding  safe: to the top of this file makes it not compile with a complaint:

Error: scope variable z assigned to non-scope b.foo

Which I think is what you expected.

As to why it happens without  safe, you may be managing your global 
variable carefully and ensuring it's unset by the time foo goes away. 
The compiler can't know.

Another reason to enable safe-by-default...

-Steve

Russ <russpowers gmail.com> writes:

On Sunday, 23 February 2020 at 03:26:17 UTC, Steven Schveighoffer 
wrote:
 On 2/22/20 10:01 PM, Russ wrote:
 Is there some newer feature I should be using?

 scope escapes are only disallowed in  safe code.

 Adding  safe: to the top of this file makes it not compile with 
 a complaint:

 Error: scope variable z assigned to non-scope b.foo

 Which I think is what you expected.

 As to why it happens without  safe, you may be managing your 
 global variable carefully and ensuring it's unset by the time 
 foo goes away. The compiler can't know.

 Another reason to enable safe-by-default...

 -Steve

Perfect, thank you! I agree that this sort of thing should be on 
by default. Better to opt-out than opt-in for memory safety.