Daniel Wallin <dalwan01@student.umu.se> writes:
David Abrahams wrote:
Daniel Wallin <dalwan01@student.umu.se> writes:
David Abrahams wrote:
Daniel Wallin <dalwan01@student.umu.se> writes:
Done now. I hate the name index_result, though. I was thinking maybe
parameter::binding<p, key, default>::type
??
Sure. Maybe we should have two, so people who want to do metaprogramming doesn't have to remove_reference<>?
binding<p, key, default>::type -> T | default binding_result<p, key, default>::type -> T& | default
?
I don't understand why you'd want the one without the reference type... and -- I'm sure it's not what you want me to focus on -- but I don't like the name "binding_result" one bit. I'm inclined to vote "no" on this one. It isn't a flexibility that's known to be needed.
I think we might be able to make it a bit safer by detecting when the default is a non-const rvalue and having p[...]
Can we really detect that?
I'm pretty sure that for all practical purposes, we can.
struct fu { template <class T> int operator|(T& x) const;
template <class T> char* operator|(T) const volatile; };
int a = 1; int x = fu() | a; char* y = fu() | 999;
Clearly you can also use a free function with enable_if to avoid the volatile interaction if you really care.
OK, cool.
There's only so much we can do. This case seems hard to get wrong for the user.
Well I guess ultimately you want a macro (ick, in this case) with decltype:
binding<p, k, decltype(some_expression)>::type x = p[x | some_expression];
right?
Ultimately I would want to write:
auto y = p[x | some_expression];
and have p[...] detect rvalues and return by value when appropriate. ;)
Well, _ultimately_ p[...] can return an rvalue reference to some_expression and avoid a copy ;-) Anyway, I'm inclined that we not try to do this by-value return thing. Your thoughts? Also: 1. for the lazy case we should probably use result_of<F()>::type on the compilers that support it? 2. We probably also need lazy_binding<p, k, f>::type, right? -- Dave Abrahams Boost Consulting www.boost-consulting.com