Don wrote:
bearophile wrote:
Don:
Yes. Actually, marking a nested function as pure doesn't make much
sense.
It's entirely equivalent to moving it outside the function; [...]
I'm not sure that nested pure member functions should be legal.
It's not fully equivalent to moving it out of the function because
once you pull it out you add a name to the outer namespace: nested
functions are useful to keep namespaces tidy too.
So I'd like to have nested pure functions too.
pure int foo(int y) { return y + y; } // outer foo
pure void bar(int x) {
pure int foo(int y) { return y * y; }
return foo(x) * .foo(x);
}
Thank you,
bye,
bearophile
That's true, but it seems quite difficult to get right. A pure nested
function can in theory access immutable members in the outer function --
but must not access the parameters of the outer function.
If there are no immutable members in the outer function, the compiler
would ideally convert it into an external pure function, so that it
doesn't need a frame pointer to the outer function. But it would need
error messages for any use of mutable outer function members. Etc.
It seems quite a lot of work for something of very limited use.
Making it into a external, private pure function is almost the same.
Actually it's not so difficult. I've created a patch for bug 2807 --
it's only 5 lines long! It gives an error message if a nested pure
function accesses a mutable variable from an outer scope.
