@safe leak fix?
Steven Schveighoffer
schveiguy at yahoo.com
Thu Nov 12 04:54:08 PST 2009
On Wed, 11 Nov 2009 16:47:10 -0500, Walter Bright
<newshound1 at digitalmars.com> wrote:
> Consider the code:
>
> @safe:
> T[] foo(T[] a) { return a; }
>
> T[] bar()
> {
> T[10] x;
> return foo(x);
> }
>
> Now we've got an escaping reference to bar's stack. This is not memory
> safe. But giving up slices is a heavy burden.
>
> So it occurred to me that the same solution for closures can be used
> here. If the address is taken of a stack variable in a safe function,
> that variable is instead allocated on the heap. If a more advanced
> compiler could prove that the address does not escape, it could be put
> back on the stack.
>
> The code will be a little slower, but it will be memory safe. This
> change wouldn't be done in trusted or unsafe functions.
This sounds acceptable to me. In response to others making claims about
modifying behavior, you can get a safe function that can use unsafe
behavior by using @trusted if you wish.
I'm assuming this behavior translates to local non-array variables?
Can we allow the scope variable hack that is afforded for delegates:
@safe int sum(scope int[] a) { int retval = 0; foreach(i; a) retval += i;
return retval;}
This would not result in a heap allocation when called with a static array.
-Steve
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