Re: [boost] boost::thread and move semantics

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2007-12-18 17:43:12

On Dec 18, 2007, at 4:12 PM, Frank Mori Hess wrote:

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> On Tuesday 18 December 2007 13:53 pm, Howard Hinnant wrote:
>> Some of this is C++0X, like the ability to return movable but non-
>> copyable items from factory functions.  Is this getting close to what
>> you were wanting to do?
>
> I think what I can do is just put a bunch of overloaded template
> constructors in my wrapper, sort of like
>
> template<typename Mutex>
> class my_mutex_wrapper
> {
> 	Mutex mut_;
> public:
> 	my_mutex_wrapper()
> 	{//...}
>
> 	template<typename A1>
> 	my_mutex_wrapper(A1 a1): mut_(a1)
> 	{//...}
>
> 	template<typename A1, typename A2>
> 	my_mutex_wrapper(A1 a1, A2 a2): mut_(a1, a2)
> 	{//...}
>
> // ...
>
> 	template<typename A1, typename A2, /*...*/, typename An>
> 	my_mutex_wrapper(A1 a1, A2 a2, /*...*/, An an): mut_(a1, a2, / 
> *...*/, an)
> 	{//...}
>
> // ...
> };
>
> One of the constructors will probably be useable by the Mutex  
> template type,
> and the invalid ones won't instantiated.

Oh, you are going to so love C++0X! :-)

template<typename Mutex>
class my_mutex_wrapper
{
        Mutex mut_;
public:
         template<typename ...Args>
        my_mutex_wrapper(Args&& ...args): mut_(std::forward<Args>(args)...)
        {//...}
};

This does several things for you:

1.  This gives you all of your constructors from the default (0 arg)  
up to 1000 args, or whatever the compiler limit happens to be (far  
more than you could ever use), with only this one constructor.

2.  The arguments will be "perfectly forwarded" without copying from  
the client of my_mutex_wrapper to your internal Mutex.  If the client  
passes in a const lvalue, the Mutex constructor will see a const  
lvalue.  If the client passes in a non-const rvalue, the Mutex will  
see a non-const rvalue.

-Howard