Re: [boost] [string_ref] degree of conformance to standard proposal

Subject: Re: [boost] [string_ref] degree of conformance to standard proposal
From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2013-12-22 20:26:01

On Dec 22, 2013, at 6:21 AM, Peter A. Bigot <pab_at_[hidden]> wrote:

> (Background: I need a string_view with features in N3762 that aren't in
> N3442 (viz., pos parameters to the string methods).  I'm trying to
> determine how much effort I should put into a set of patches to update
> the Boost implementation to the latest draft proposal.)
> 
> The default constructor for Boost.string_ref produces an object which
> returns a null pointer from data().  N3442 and its successor N3762 both
> require the return value from data() to be non-null
> (http://isocpp.org/files/papers/N3762.html#h5o-5).

Yeah; I’ve spoken to Jeffrey (author of the proposal) and will be filing a defect report about that.

> GCC's libstdc++ folks solved this by adding a constexpr unit length
> string to serve as the base referenced object
> (http://gcc.gnu.org/ml/libstdc++/2013-11/msg00104.html).  But for Boost
> I don't see how this can be changed without introducing a link
> dependency.

Right.

Not to mention that if you initialize a string_ref ( NULL, 0 )
then requiring its’ data() call to return non-null means extra code.

If the length of the string_ref is 0, then the return value of data() is meaningless; you can’t do anything useful with it.

* You can’t dereference it, any more than you can dereference the end() iterator of a vector.
* You can’t compare it to a pointer in another container (undefined behavior).
* You can compare it with NULL, but what does that tell you?

> In a cases like this, how closely does Boost want to track the standard
> proposals?
> 
> Similarly, the standard proposal has settled on *string_view instead of
> *string_ref.  Would Boost rename the library/class, or just introduce an
> alias?

I have that on my to-do list.

My thought is to rename the classes to match the standard, but keep the string_ref typedefs for compatibility.
[ I’m open to other suggestions. ]

I will happily consider patches for the missing features.
[ Though my opinion is that replicating the entire interface of std::string in string_[ref|view] is a mistake ]

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists_at_[hidden]>

A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait).
        -- Yu Suzuki