Andrei Alexandrescu wrote:
Justin Johansson wrote:
Justin Johansson wrote:
aarti_pl wrote:
Andrei Alexandrescu pisze:
aarti_pl wrote:
aarti_pl pisze:
Andrei Alexandrescu pisze:
2. User-defined operators must be revamped. Fortunately Don
already put in an important piece of functionality (opDollar).
What we're looking at is a two-pronged attack motivated by Don's
proposal:
http://prowiki.org/wiki4d/wiki.cgi?LanguageDevel/DIPs/DIP7
The two prongs are:
* Encode operators by compile-time strings. For example, instead
of the plethora of opAdd, opMul, ..., we'd have this:
T opBinary(string op)(T rhs) { ... }
The string is "+", "*", etc. We need to design what happens with
read-modify-write operators like "+=" (should they be dispatch
to a different function? etc.) and also what happens with
index-and-modify operators like "[]=", "[]+=" etc. Should we go
with proxies? Absorb them in opBinary? Define another dedicated
method? etc.
* Loop fusion that generalizes array-wise operations. This idea
of Walter is, I think, very good because it generalizes and
democratizes "magic". The idea is that, if you do
a = b + c;
and b + c does not make sense but b and c are ranges for which
a.front = b.front + c.front does make sense, to automatically
add the iteration paraphernalia.
(..)
Andrei
I kinda like this proposal. But I would rather call template like
below:
T opInfix(string op)(T rhs) { ... }
T opPrefix(string op)(T rhs) { ... }
T opPostfix(string op)(T rhs) { ... }
and allow user to define her own operators (though it doesn't
have to be done now).
I know that quite a few people here doesn't like to allow users
to define their own operators, because it might obfuscate code.
But it doesn't have to be like this. Someone here already
mentioned here that it is not real problem for programs in C++.
Good libraries don't abuse this functionality.
User defined operators would allow easy definition of Domain
Specific Languages in D. I was already writing about it some time
ago:
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=81026
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=81352
BR
Marcin Kuszczak
(aarti_pl)
Of course for opPrefix/opPostfix signatures will be different:
T opPrefix(string op)() { ... }
T opPostfix(string op)() { ... }
Sorry for mistake.
BR
Marcin Kuszczak
(aarti_pl)
I think we'll solve postfix "++" without requiring the user to
define it. Do you envision user-defined postfix operators?
Andrei
Well, maybe something like below:
auto a = 2²; //(quadratic power of 2)
auto a = 5!; //factorial of 5
auto a = 2Ƴ + 3ɛ; //solving equations
auto weight = 5kg; //units of measurement
The point is that this covers whole scope of operators. In fact even
built-in operators could be defined using it.
Postfix operator ++ can be defined using prefix operator++ just by
delegation and this can be default.
Best Regards
Marcin Kuszczak
(aarti_pl)
Marcin demonstrates a valid point.
If there is going to be this feature creep, the feature should be
complete with all the usual variants of operator arity and notation
(i.e. prefix/postfix/infix). Otherwise it really it's only
two-thirds baked.
-- Justin Johansson
I meant to say "Iff there is ..." as in "if and only if".
Like others, I'm not completely sold on the idea at all. Also it's
probably not possible to squeeze something as long as this on to a
short list.
All or nothing please.
I disagree with this false choice.
http://en.wikipedia.org/wiki/False_dilemma#False_choice
Andrei
You are very well read :-)
