On 12/13/2011 07:26 AM, Walter Bright wrote:
On 12/12/2011 10:56 AM, Steven Schveighoffer wrote:
If this ends up being viable, this is actually easier to explain than the
current rules for inout. We just have to make sure the rules are sound
before
doing something like this.
I don't understand the point of doing this. Just make it const.
It does not work with const. (the fact that it currently does with DMD
is a severe bug).
Consider:
void bad(const(int)** x, const(int)* y){ *x=y; }
void main(){
immutable(int) i = 1;
int* x;
bad(&x, &i); // should error int** does not convert to const(int)**
// currently:
assert(x is &i); // mutable reference to immutable data
*x = 2; // BOOM!
}
On the other hand:
void main(){
immutable(int) i = 1;
immutable(int)* x;
bad(&x, &i); // fine, but the type checker cannot know that
}
Therefore it is sensible to allow
void good(inout(int)** x, inout(int)* y){ *x=y; }
void main(){
immutable(int) i = 1;
int* x;
good(&x, &i); // error, no value for inout makes this typecheck
}
On the other hand:
void good(inout(int)** x, inout(int)* y){ *x=y; }
void main(){
immutable(int) i = 1;
immutable(int)* x;
good(&x, &i); // this can now typecheck: use inout as immutable
}
