Re: initial function of boost::thread

From: Mark Sizer (yg-boost-users_at_[hidden])
Date: 2003-05-19 13:01:09

This is _NOT_ your fault. You've created an excellent library and do a 
great job of support on this list.

I'm a very old-school C++ person (I started with C-Front) and a lot of 
Boost concepts are new to me (e.g. function objects, I don't even want 
to think about the lambda stuff). I dove off the deep end on this 
project. I should have done more research.

The examples will be great (I got the distribtion, I haven't even looked 
in CVS - that's the pointer I needed).

Thanks,
  - Mark

William E. Kempf wrote:

> Mark Sizer said:
> 
>>This is also stuff that has been answered before. I really have
>>searched. Links to the answers will be as appreciate as an inline
>>responses.
>>
>>I've been using free file-scoped functions up to now because I really
>>don't understand what a boost::function0<void>& is.
>>
> 
> It's a "function object" which takes no parameters and returns nothing. 
> Function pointers are valid "function objects", but so are class instances
> with an overloaded operator().
> 
> 
>>I get, I think, that it can't be a member function, because there is no
>>'this' attached.
>>
> 
> Not directly, however boost::bind can be used to create a function object
> that does call a member function.
> 
> 
>>However, I'm having trouble with two things:
>>
>>#1 from: function.tutorial.html
>><quote>
>>   boost::function2<float, int, int> f;
>>
>>   struct int_div {
>>     float operator()(int x, int y) const { return ((float)x)/y; };
>>   };
>>
>>   f = int_div();
>></quote>
>>
>>operator() _is_ a member function. When assigning int_div() to f, which
>>of potentially zillions of instances of int_div is being referenced? Is
>>a new one created on invocation? (the example uses std::cout << f(5,2)
>><< endl;)
>>
> 
> The syntax "int_div()" is a call to the int_div constructor.  So, 'f' is
> being assigned to a new instance of int_div.  This can be done, because
> int_div *is a function object* who's signature matches that required by
> boost::function2<float, int, int>.
> 
> 
>>I'm missing a theoretical bit of information that makes this hang
>>together. Help, please.
>>
>>#2 from:
>>http://www.cuj.com/articles/2002/0205/0205a/0205a.htm?topic=articles
>><quote>
>>  However, because Boost.Threads uses a function object instead of just
>>a function pointer, it is possible for the function object to carry data
>> needed by the thread. This approach is actually more flexible and is
>>type safe. When combined with functional libraries, such as Boost.Bind,
>>this design actually allows you to easily pass any amount of data to the
>> newly created thread.
>></quote>
>>
>>BUT HOW?!?! Any pointers (with many examples, please) would be much
>>appreciated.
>>
> 
> $BOOST_ROOT/libs/thread/tutorial/helloworld4.cpp illustrates using
> Boost.Bind to pass data while creating a thread.
> 
> Sorry for the frustration.  I need a full tutorial in the documentation,
> so this isn't something that's your fault, but mine.  For now, all I can
> recommend is that you look at the numerous example programs included in
> the CVS archive.
> 
>