Some people use ref for performance to prevent the copying that
must occur when passing by value. I propose a small optimisation
to make this unnecessary in a bunch of cases.
At the ABI level (no change in language semantics), if a given
parameter would otherwise be copied and passed on the stack:
1) immutable parameters to all functions are passed by reference
2) const parameters to pure functions are passed by reference, if
and only if all other parameters - including any implicit this
parameter - contain no mutable references (otherwise "weakly"
pure functions could modify the data we are now referring to
instead of having copied, changing semantics).
The main benefit from this would be:
class C
{
void doSomething(const float[16] m0) const pure
{
// ...
}
void doSomethingElse(immutable float[16] m1)
{
// ...
}
}
void foo(C c, float[16] m0, immutable float[16] m1)
{
// ...
c.doSomething(m0); // no copying of m0 here
c.doSomethingElse(m1); // or m1 here
// ...
}
I presume this has been thought of before, is there a reason why
we don't do it already? I guess 2) is a bit complicated, but 1)
is easy.
