On Thursday, 16 June 2016 at 13:54:11 UTC, MMJones wrote:
Suppose one has something like
class foo
{
int[] x;
void bar()
{
x = [];
}
}
Does the GC trash the "cache" when calling bar or does it
realize that it can use the same memory for x and essentially
just shortens the array?
Is it equivalent to setting length = 0?
I'm a bit worried that setting a managed array to [] might
cause a completely new reallocation, which is unnecessary and
undesirable.
To prevent confusion, here's a related example:
void foo()
{
int[] x = [1,2,3];
x = [4];
}
in theory, the first allocation (for [1,2,3]) could be avoided.
It wouldn't be the GC doing it though, it would just be the
optimiser eliminating the redundant initialisation of x.
However:
class C
{
int[] x;
this()
{
x = [3,2,1];
}
void foo()
{
x = [0];
}
}
auto bar()
{
auto c = new C;
auto localX = c.x;
c.foo();
return localX;
}
the initialisation of c.x is no longer redundant, because the
memory is referenced by localX, so a new allocation is necessary
in foo.
P.S. remember that D's arrays/slices aren't "managed" as such.
Only the memory backing them is managed, and then only if the
memory was allocated by the GC.
