Re: [boost] [fusion] value_of tranform_view

From: Peter Dimov (pdimov_at_[hidden])
Date: 2007-07-13 08:02:23

Tobias Schwinger wrote:
> Peter Dimov wrote:
>> Stjepan Rajko wrote:
>>
>>> [comes to a screeching halt from changing code]
>>
>> Yep. :-)
>
> Sorry for the false alarm!
>
>>> I'm still not entirely on very sure footing when it comes to rvalues
>>> and lvalues, so can I bother you with a practical clarification?
>>>
>>> So, if I have, say, a function object with operator()(int &), I
>>> should specify result<F(int &)>, (but maybe if I have
>>> operator()(const int &), or operator()(int), I can specify
>>> result<F(int)>?)
>>
>> If you have operator()( int& ), you need result<F(int&)>. If you have
>> operator()( int ), you need both result<F(int)> and result<F(int&)>
>> because your operator() can take either an lvalue or an rvalue.
>
> We'd also need 'int const &' (given we don't just provide
> 'result_type' or deduce whatever it is), right?

And bool, and char, and double, and so on; every argument type that can be 
passed to operator(). It's not practical to enumerate everything. But to 
answer your question, yes, a const lvalue of type int is a valid argument 
and needs to be supported by your specialization/result.