Re: Nested functions should be exempt from sequential visibility rules

[Don Clugston]

On 03/04/12 12:32, Timon Gehr wrote:
On 04/03/2012 10:27 AM, Don Clugston wrote:
On 03/04/12 07:38, Nick Sabalausky wrote:
Regarding this:
http://d.puremagic.com/issues/show_bug.cgi?id=790

I submit that nested functions should be exempt from the usual
sequential
visibility rules. (Therefore, mutually recursive nested functions would
become possible.)

Or at the very *least*, this horrific C-like workaround should be
possible:

void foo()
{
void b();
void a() {...};
void b() {...};
}

...Flame away! ;)


This is asking for a complicated special case. In global scope, order of
declarations doesn't matter. In function scope, order of declarations
always matters.
If you have type inference of function returns, things can get nasty:

void foo()
{
auto b() { return a(); }
X x = whatever;
auto a() { return x; }
}
Now b actually depends on the declaration of x. So it's not enough to
say that only function declarations are immune to ordering rules.

I come to a different conclusion. If only function declarations are
immune to ordering rules, the above example is simply illegal. The
example cannot be used to demonstrate incompleteness of the approach.

I don't see a way to just declare it as "illegal". How would you detect 
that situation in the general case?
It's not easy.

Y b() { ... }
Y y = b();
X x = ...

Prove that y doesn't depend on x.