Jérôme M. Berger wrote:
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Daniel Keep wrote:
Michiel Helvensteijn wrote:
[Condensed: syntax sucks, let's introduce more!]
I might be old fashioned (get offa mah lawn!), but I've always found
something like the following quite acceptable:
class Foo
{
mixin(properties
("
rw int bar;
ro float baz;
wo Foo zyzzy;
"));
}
Note that this is a very limited use for properties. Defining
properties isn't just a question of access control (read/write, read
only, or write only).
For me, it *was* a case of access-control... at least, it was about 80%
of the time.
I'm a fan of interface-heavy design: make an interface for every
distinct kind of functionality and pack them all together. That means I
end up with a metric buttload (equivalent to about 42 imperial piles) of
properties.
And most of them were just accessors that needed to be in the interface;
hence the functionality of the mixin.
> It is also a way to execute arbitrary code
each time the value is changed (or accessed), ...
It's been a while since I used the code, and honestly I can't seem to
track it down, but I recall that I could do this:
mixin(properties(" rw int bar; "));
protected void bar_onSet(int newValue) { ... }
There was also an *_onGet, and you could block setting a property by
throwing an exception, I believe.
Granted, this doesn't cover every possible use-case, but then it's not
supposed to; it's supposed to make the 90% easier. It still did the
assignment, since I felt you shouldn't be making properties that have a
setter that doesn't set anything...
> ... or to create
properties that don't correspond to actual data fields (complex
module and argument come to mind).
If the property doesn't correspond to a physical field, then you're
going to have to write the code to handle it from scratch. And no
matter WHAT you do, it's eventually going to boil down to one or more
functions. Which is EXACTLY how they currently work.
What would be the point of making a special syntax when you can already
do that? :P
> How would you do that with
mixins? (Not that it would be impossible, but the syntax would
probably be horrible).
Jerome
On a somewhat related note, I've often pondered writing a very limited D
parser in CTFE to do this sort of thing more easily, but never got
around to it, nevermind the CTFE memory bugs...
-- Daniel
