On 2015-02-27 20:34:08 +0000, Steven Schveighoffer said:
On 2/27/15 3:30 PM, Steven Schveighoffer wrote:void main() { C c = new C; // ref counted class C2 c2 = new C2; // another ref counted class c2.c = c; foo(c, c2); }Bleh, that was dumb. void main() { C2 c2 = new C2; c2.c = new C; foo(c2.c, c2); }Still same question. The issue here is how do you know that the reference that you are sure is keeping the thing alive is not going to release it through some back door.
You have to retain 'c' for the duration of the call unless you can prove somehow that calling the function will not cause it to be released. You can prove it in certain situations:
- you are passing a local variable as a parameter and nobody has taken a mutable reference (or pointer) to that variable, or to the stack frame (be wary of nested functions accessing the stack frame) - you are passing a global variable as a parameter to a pure function and aren't giving to that pure function a mutable reference to that variable. - you are passing a member variable as a parameter to a pure function and aren't giving to that pure function a mutable reference to that variable or its class.
There are surely other cases, but you get the idea. These three situations are probably the most common, especially the first one. For instance, inside a member function, 'this' is a local variable and you will never pass it to another function by ref, so it's safe to call 'this.otherFunction()' without retaining 'this' first.
-- Michel Fortin michel.for...@michelf.com http://michelf.com/
