Re: inout and function/delegate parameters

[Timon Gehr]

On 02/19/2012 11:27 PM, kenji hara wrote:

I think the 'scope' keyword may resolve issue.

Attributes of lazy parameter in template function belong to caller side.

int foo()(lazy int value) @safe pure /*nothrow*/ { return value(); }
void main() {
     int n = foo(10);
     // evaluating lazy parameter never break safety and purity of foo.
     // (violating nowthrow-ness might be a bug.)
     // because the violation belongs to caller side - it is main function.
}

Similarly, scope delegate body always in caller side, so calling it
means temporary exiting to caller side.

void foo(ref inout int x, scope void delegate(ref inout(int)) dg) {
     dg(x);
}
void main() {
     int a;
     foo(a, (ref int x){ x = 10; });  // don't break foo's inout-ness,
so should be allowed
     assert(a == 10);
}

How about?

Kenji Hara

If I get you right, then this cannot work in general.

immutable int y=0;
void foo(ref inout int x, scope void delegate(ref inout(int)) dg) {
    dg(y); // boom
}