On 20.06.2011 7:56, Paul D. Anderson wrote:
Jonathan M Davis Wrote:
For instance, if I want to make it legal to pass a core.time.TickDuration to
to!(core.time.Duration) instead of casting it (which is actually why I've been
think of this issue), what is the standard way to do that? Or isn't there one?
I'm not aware of one. And if there isn't one, how should we do it?
I can think of 3 possible ways:
1. Overload to in the module with the type being converted from. So, for
instance, core.time would have an overload for to which takes a TickDuration
and returns a Duration (either that or std.datetime if it didn't work to have
that in druntime for some reason). I'm not sure if that'll cause problems with
overload sets or not though.
2. Make it so that std.conv.to can do its thing based on opCast. If a type
overloads opCast, then std.conv.to can use that opCast to do the conversion
(but only if opCast is defined, not for just any cast which may or may not be
valid).
3. Make it so that user-defined types have a semi-standard member function
(e.g. to) which std.conv.to looks for and uses for conversions if it's there.
Which of those would you consider to be the best? Or can you think of another,
better way? It seems to me that we need an essentially standard way of
defining conversions which use to. Otherwise, the only option is to use
opCast, and while there's nothing wrong with overloading opCast, it would
definitely be preferable to use to for safe conversions.
Thoughts?
- Jonathan M Davis
I'd also like to see a solution to this, primarily because std.conv.to is so
useful.
I don't think #1 works. At least, I've tried it and it gets confused on
overloading. But maybe I didn't do it right. Along this same line, is there a
way to write a ToImpl that std.conv can recognize? Again, I've tried this
without success, but that doesn't mean it can't be done.
#2 is problematic because I might want to to! things I might not want to cast
to. But it would be better than nothing.
I'd vote for #3. It's not much different than having std.conv look for a
toString() function, which is great for to!string
In my case, I've created an alternative conversion module and only implemented
the types I need; then I've added the types I defined. But I know this will
bite me when I try to integrate with other modules.
I don't care much how this is implemented but it would be a very useful tool.
Paul
I think option #3 could be great, and the name of that templated
function could be ... to!
--
Dmitry Olshansky
