On Thu, 16 Feb 2012 21:49:40 -0500, Walter Bright
<newshou...@digitalmars.com> 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 think it feels like a (welcome) about face from previous stances. But I
share some concern with others in that we are separating the attributes of
a function from its declaration to the point where we need a tool to
determine what the exact attributes of a function are.
I shudder to think about how I would understand some of the CSS I have to
deal in my daily work if I didn't have firebug. I hope D doesn't become
similar.
Of course, if we get to the point where DDoc is full-featured, one will
almost never have to look at function declarations when using them.
Also, I like how you *can* repeat the attributes if it's necessary to.
Could there be a compiler option for requiring overriding functions to
repeat base attributes? Or at least print out where they are while
compiling? At least then you can see where your attributes aren't
repeated.
-Steve
