Re: [Boost-users] [Boost.Assign] list_of::range without an initial (single) element?

Subject: Re: [Boost-users] [Boost.Assign] list_of::range without an initial (single) element?
From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2010-06-17 07:53:39

Michael McNeil Forbes skrev:
> Thorsten Ottosen wrote:

>> Just to be clear, you want list_of() to be empty_list_of<*any 
>> type*>(), and for the type of the list to be deduced by the first 
>> argument:
>>
>>  list_of()(42);
>>
>> would be a list of ints with one value (42).
> 
> This is what I was expecting when I first started.  Semantically this 
> behaviour seems to make sense, but I have not thought too deeply about it.
> 
>> If so, I think this syntax is possible, but I am worried that the 
>> difference between list_of() and list_of<T>() is too subtle.
> 
> What exactly would be the subtle difference between these two?   Would 
> they not both be forms of empty lists, except the second form would only 
> accept arguments of type T?

Currently list_of<int>() is not an empty list.

> The other thing I was expecting was perhaps an exposed range() function 
> so that one can just go:
> 
> ... = range(a).range(b)
> 
> (I also thought that the exposed repeat() functions would also allow for 
> this:
> 
> boost::array<int, 4> c = boost::assign::repeat(4, 5);
> 
> use but I apparently do not understand yet how the exposed repeat is 
> intended to be used.)

array has a fill member for that purpose, albeit it lacks a constructor.
No, repeat() and range() are used inside lists:

push_back( vec ) += 1,2,3,repeat(4,5),range(other_rng),5,6,7;

> I have to look more deeply into the new proposal for operator&&(), but 
> it seems a little specific.  Is there no way that the ideas discussed 
> here could be made as efficient, requiring a separate operator&&() for 
> chaining?  As a user, I would not mind being steered towards the 
> efficient usage if documented properly.

The new methods are quite efficient. In the old library, list_of<T>() is 
not efficient (ease of use is the key goal here), whereas 
ref_list_of<T>()/cref_list_of() are.

-Thorsten

-Thorsten