Sergey Kovrov wrote:
On 3/9/2009 8:50 PM, Chris Nicholson-Sauls wrote:
While not strictly intuitive, you could do this:
auto var = Rebindable!(const Foo)(new Foo);
assert(var.opDot !is null);
As 'opDot' returns the wrapped object (with const intact). The downside
to that, however, is that it won't work in those cases where
Rebindable's template parameter was mutable, as then it simply aliases
it. This shouldn't be a problem in general use, though. Only in generic
code, which could try to check for Rebindable.
Thanks Chris, this approach indeed works, its a shame I haven't figured
this on my own.
I wonder if it's proper usage of opDot.. In general, is it safe for
client code to rely on implementation of opDot and call it directly?
Technically, no, not really. Then again, it isn't absolutely horrible
either. It would be better if there were some other means of testing
for null, which could be overwritten. The only alternative that comes
immediately to mind would be an opCast to T, but then it would supersede
any opCast defined on T. (Then again, in code dealing with Rebindable
one could always chain the casts: 'cast(Bar)cast(Foo)var'. Ugly, but
possibly effective.
And in this particular case we rely on the fact that Rebindable uses
opDot to forward calls.
Considering its the only way of doing so in a completely generic manner
anyhow, I don't think its a big deal. It could become annoying,
however, for generic code.
Slightly off-topic... In Python world (and I guess any other dynamic
language) it is not valid to make assumptions based on implementation.
Only safe way to use "foreign code" (a library, framework) is to follow
documentation. That way authors of libraries are free to change their
code as long as it comply with documented behavior.
-- serg.
The sentiment applies in almost any language, but a static typed
language does allow for a few more assumptions. I have a habit of
crawling through the sources of libraries I use anyhow, so I'm sure I
occasionally do things in "*evil*" undocumented ways. ;)
Maybe there should be an 'IsNull' template that understands
Rebindable's. That said, I'm not sure what kind of is() invocation
would match a struct template... (pssst, template ninjas...)
-- Chris Nicholson-Sauls
