[Issue 3925] Missed escaping reference of a local variable
https://issues.dlang.org/show_bug.cgi?id=3925 Nick Treleaven changed: What|Removed |Added Status|NEW |RESOLVED CC||n...@geany.org Resolution|--- |FIXED --- Comment #8 from Nick Treleaven --- All code samples here fail to compile with @safe and -dip1000, dmd v2.079.1, except this one: (In reply to Michel Fortin from comment #3) > There is a similar problem with delegates: I looked to see if this is filed, the closest I could find is Issue 18738, which is strongly related. Closing this. --
[Issue 3925] Missed escaping reference of a local variable
http://d.puremagic.com/issues/show_bug.cgi?id=3925
--- Comment #7 from bearophile_h...@eml.cc 2011-06-29 15:32:18 PDT ---
Two more cases of undetected escaping of reference:
int* ptr;
void foo1() {
int local;
ptr = &local;
}
void foo2(int** x) {
int i;
*x = &i;
}
void main() {}
See also bug 5541 and bug 1313
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[Issue 3925] Missed escaping reference of a local variable
http://d.puremagic.com/issues/show_bug.cgi?id=3925
--- Comment #6 from bearophile_h...@eml.cc 2010-10-25 15:40:48 PDT ---
(In reply to comment #5)
> ---
> class A{}
>
> A foo(A a)
> {
> return a;
> }
>
> A bar()
> {
> scope A a=new A();
> return foo(a);
> }
> ---
The "scope" is deprecated, so I think yours isn't a valid error case, sorry :-(
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[Issue 3925] Missed escaping reference of a local variable
http://d.puremagic.com/issues/show_bug.cgi?id=3925
--- Comment #5 from Sobirari Muhomori 2010-10-25
13:59:45 PDT ---
---
class A{}
A foo(A a)
{
return a;
}
A bar()
{
scope A a=new A();
return foo(a);
}
---
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[Issue 3925] Missed escaping reference of a local variable
http://d.puremagic.com/issues/show_bug.cgi?id=3925
--- Comment #4 from bearophile_h...@eml.cc 2010-10-22 19:26:06 PDT ---
Here DMD 2.049 doesn't find the error, but it should:
int* foo() {
int x;
int* p = &x;
return p;
}
void main() {}
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[Issue 3925] Missed escaping reference of a local variable
http://d.puremagic.com/issues/show_bug.cgi?id=3925
Michel Fortin changed:
What|Removed |Added
CC||michel.for...@michelf.com
--- Comment #3 from Michel Fortin 2010-03-10
15:04:05 EST ---
(In reply to comment #2)
> I've just been dealing with ref returns in my recent CTFE patch. But I don't
> think it's very complicated.
> As far as I can tell, ref returns are only a problem if a local variable is
> passed as a ref parameter, or if it is a member function of a local struct.
> If either of those is true, it should be considered to potentially be a return
> of a local variable.
> I don't think there's any problem with foo, but bar should generate an error.
This seems fair. There is a similar problem with delegates:
@safe
void delegate() foo(ref int a) {
return { writeln(a); };
}
@safe
void delegate() bar() {
int a;
return foo(a); // leaking reference to a beyound bar's scope
}
It could be solved in the same way.
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[Issue 3925] Missed escaping reference of a local variable
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Don changed:
What|Removed |Added
CC||clugd...@yahoo.com.au
--- Comment #2 from Don 2010-03-10 11:12:03 PST ---
(In reply to comment #1)
> This was the original code by Michel Fortin:
>
> @safe ref int foo(ref int a) {
> return a;
> }
> @safe ref int bar() {
> int a;
> return foo(a);
> }
>
>
> Norbert Nemec comments:
> >I would say the possibility of a bug makes this code unsafe by definition.
> >Ref returns must be considered unsafe by default, unless the compiler can
> >know for sure that the object will exist beyond the lifetime of the
> >function.<
>
>
> So I think Norbert Nemec idea is: while the normal compiler error messages
> assume correctness and need a demonstration of unsafety to be shown, @safe can
> do the opposite assuming unsafety and requiring a demonstration of safety.
I've just been dealing with ref returns in my recent CTFE patch. But I don't
think it's very complicated.
As far as I can tell, ref returns are only a problem if a local variable is
passed as a ref parameter, or if it is a member function of a local struct.
If either of those is true, it should be considered to potentially be a return
of a local variable.
I don't think there's any problem with foo, but bar should generate an error.
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[Issue 3925] Missed escaping reference of a local variable
http://d.puremagic.com/issues/show_bug.cgi?id=3925
--- Comment #1 from bearophile_h...@eml.cc 2010-03-10 10:08:04 PST ---
This was the original code by Michel Fortin:
@safe ref int foo(ref int a) {
return a;
}
@safe ref int bar() {
int a;
return foo(a);
}
Norbert Nemec comments:
>I would say the possibility of a bug makes this code unsafe by definition. Ref
>returns must be considered unsafe by default, unless the compiler can know for
>sure that the object will exist beyond the lifetime of the function.<
So I think Norbert Nemec idea is: while the normal compiler error messages
assume correctness and need a demonstration of unsafety to be shown, @safe can
do the opposite assuming unsafety and requiring a demonstration of safety.
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