On 2/16/12 8:49 PM, Walter Bright wrote:
Given:class A { void foo() { } } class B : A { override pure void foo() { } } This works great, because B.foo is covariant with A.foo, meaning it can "tighten", or place more restrictions, on foo. But: class A { pure void foo() { } } class B : A { override void foo() { } } fails, because B.foo tries to loosen the requirements, and so is not covariant. Where this gets annoying is when the qualifiers on the base class function have to be repeated on all its overrides. I ran headlong into this when experimenting with making the member functions of class Object pure. So it occurred to me that an overriding function could *inherit* the qualifiers from the overridden function. The qualifiers of the overriding function would be the "tightest" of its explicit qualifiers and its overridden function qualifiers. It turns out that most functions are naturally pure, so this greatly eases things and eliminates annoying typing. I want do to this for @safe, pure, nothrow, and even const. I think it is semantically sound, as well. The overriding function body will be semantically checked against this tightest set of qualifiers. What do you think?
I thought about this for a while and seems to work well. The maintenance scenarios have already been discussed (people add or remove some attribute or qualifier) and I don't see ways in which things become inadvertently broken.
The const qualifier is a bit different because it allows overloading. Attention must be paid there so only the appropriate overload is overridden.
Congratulations Walter for a great idea. Inference is definitely the way to go.
Andrei
