2013/4/28 Walter Bright <newshound2@digitalmars.com>

On 4/27/2013 3:58 PM, Walter Bright wrote:

On 4/27/2013 1:26 PM, kenji hara wrote:

I don't have so much knowledge about C/C++ language spec, but for the issue case
C++ makes "ambiguous error".

That's because C++ regards an implicit conversion of 1 to bool or long as having
equal weight, and it has no further mechanism.

Note that the following is also ambiguous in C++:

void foo(bool b) { }
void foo(long l) { }

void main() {
foo(3);
}

Yes, but all C++ users would accept the behavior - In C++, all integer types are treated as bool type under the rule that zero/non-zero value is equivalent to false /true. From the view of D user, it looks inconvenient, but there is still few and consistent rule.

On the other hand, D looks like having *special rule* of 0 and 1 literal for boolean type. Even if the underlying rule is sane (partial ordering rule and VRP), the combination makes weird behavior.

----

Now I doubt that this problem comes from the history of D and wrong dmd implementation. In early D1 age, we had had 'bit' type which exactly have one bit value 0 and 1. After the while, the name 'bit' changed to 'bool'. At that point, 'bool' was kept the characteristics that it is one of the integer types - even though we should discard it. Right?

VRP is a new concept that introduced in D2 age. But, maybe, the combination of bool and VRP had not been considered enough. So now problem is appeared there.

Now it feels to me that is a debt from D1.

Kenji Hara