On Friday, 17 February 2012 at 03:24:50 UTC, Jonathan M Davis
wrote:
On Thursday, February 16, 2012 18:49:40 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?
No. Absolutely not. I hate the fact that C++ does this with
virtual. It makes it so that you have to constantly look at the
base classes to figure out what's virtual and what isn't. It
harms maintenance and code understandability. And now you want
to do that with @safe, pure, nothrow, and const? Yuck.
I can understand wanting to save some typing, but I really
think that this harms code maintainability. It's the sort of
thing that an IDE is good for. It does stuff like generate the
function signatures for you or fill in the attributes that are
required but are missing. I grant you that many D developers
don't use IDEs at this point (at least not for D) and that
those sort of capabilities are likely to be in their infancy
for the IDEs that we _do_ have, but I really think that this is
the sort of thing that should be left up to the IDE. Inferring
attribtutes like that is just going to harm code
maintainibility. It's bad enough that we end up with them not
being marked on templates due to inferrence, but we _have_ to
do it that way, because the attributes vary per instantiation.
That is _not_ the case with class member functions.
Please, do _not_ do this.
- Jonathan M Davis
In the situation where the IDE writes it for you, said IDE will
help you only when you write the code.
In the situation where the IDE tells you what they are (through
something like hovering over it), it will help you no matter who
writes the code. It is also significantly easier to implement,
particularly taking into consideration things like style,
comments, etc.
