Re: [boost] Lambda Library

From: Jaakko Jarvi (jajarvi_at_[hidden])
Date: 2002-02-07 16:06:51

> Well, I was unable to compile with gcc 3.0.3 (cygwin) and 2.95.3
> (mingw). All test I've tried gave the same errors:
 ...
> 
> The offending line in actions.hpp is
> 
>   BOOST_STATIC_CONSTANT(bool, value =
>   (boost::is_base_and_derived<protectable, T>::value)); 
> 
> I'm using boost v 1.26.0. Do I need the current CVS sources?

Oh yes. is_base_and_derived was only added in January. :(

> " ... the lambda expression _1 + 1 can be seen as syntactic sugar
> for the pseudo code bind(operator+, _1, 1). "
> 
> Should be "... the lambda expression 1 + _1 ...". This way the order
> of arguments is the same for both expressions. Note that you later
> define an asymmetric operator+ in another example.

Can you elaborate this? I can't see what is wrong with the argument 
orderging? 

> 
> "for_each(v.begin(), v.end(), _1 = bind(foo, _1));"
> 
> 'for_each' is a non-mutating algorithm. 'transform' is better for this
> case.

Yes, for_each only requires the iterators to be InputIterators and I guess 
that is why it is listed as non-modifying sequence operation.

I'm not sure what to do with this. To me code like this

  for_each(a.begin(), a.end(), ++_1); 

compared to this

  transform(a.begin(), a.end(), a.begin(), _1 + 1);

looks more intuitive.

Both will work, but the former may be (mis)using for_each in a 
non-conformant way.

We can always define 

lambda::for_each 
 
with a less constraining requirements to go around this :)

> (1) Having recursion would be great.
> > (2) Having some kind of 'let' form 
Something to think about :)

Thanks for the comments, Jaakko