On 02/26/2012 06:39 PM, Jason House wrote:
On Friday, 17 February 2012 at 02:49:40 UTC, 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'm still not convinced about this apply to const. Consider this example:
Initial code:
class A{
void foo(int) const;
void foo(float) const;
}
class B{
alias A.foo foo;
override void foo(int);
}
Revision to class A:
class A{
void foo(int);
void foo(int) const;
void foo(float);
void foo(float) const;
}
When the user recompiles, there will be no errors or warnings. All uses
of foo(int) through a const B will revert to using the base class's
implementation.
This is by far not the only hijacking scenario enabled by using alias
for merging in the parent's overload set. re-implementing the method and
calling super is the only safe way to warrant hijacking protection.
