On 11/15/17 9:43 AM, Dr. Assembly wrote:
I'm learning to use interface with contracts. In below code, in isn't
being "called". Can someone point out why? what am I doing wrong?
void main() {
C c = new C();
writeln(c.foo(1));
}
interface I
{
int foo(int i)
in { assert(i > 2); }
out (result) { assert(result != 0); }
void baa();
}
class C : I
{
int foo(int i) {
return i * 2;
}
void baa() {
writeln("Hello!");
}
}
Not going to defend these design decisions, but according to
https://dlang.org/spec/contracts.html#in_out_inheritance:
1. If a function in a derived class overrides a function in its super
class, then only one of the in contracts of the function and its base
functions must be satisfied. Overriding functions then becomes a process
of loosening the in contracts.
2. A function without an in contract means that any values of the
function parameters are allowed. This implies that if any function in an
inheritance hierarchy has no in contract, then in contracts on functions
overriding it have no useful effect.
So simply overriding a function and specifying no in contract cancels
all in contracts.
I don't think there's a way to specify inheriting the in contract. I
believe the only correct way to do this is to repeat the base's in contract.
-Steve
