Re: [boost] [string_ref] type erasure to support arbitrary strings

Subject: Re: [boost] [string_ref] type erasure to support arbitrary strings
From: Jeffrey Lee Hellrung, Jr. (jeffrey.hellrung_at_[hidden])
Date: 2013-01-30 12:35:54

On Wed, Jan 30, 2013 at 5:16 AM, Andreas Pokorny
<andreas.pokorny_at_[hidden]>wrote:

> Hi,
> When I made a first glance of the proposal I expected that string_ref
> is some kind of type erasing non owning holder of a reference to an
> arbitrary string class. The imperfect silver bullet for the diversity
> of string types.
>
> Take a project that uses c++ libraries using std::string, Qt GUI and
> maybe a module that works with chunked strings (string composed out of
> a list of usually equally sized blocks of memory). At the boundaries
> of the software modules copies have to occur. Frequently the interface
> expects some kind of constant references to a certain string type.
> Most of the time the callee just wants to process the complete string
> or just a part of the string. So there might not even be the necessity
> to have random access hence no need for a contiguous copy of the
> string contents.
>
> Thats why I would prefer a facility that only requires that the source
> string is a forward range of characters in an arbitrary encoding.
>
> I do not think that it makes sense to only address contiguous
> sequences of characters.
>

It's somewhat of a compromise as a string_ref has very little access
overhead compared to using a std::string or similar directly (I would think
the only overhead, if any, is in the construction of the string_ref). A
type-erased reference to a range of characters would have quite a bit of
access overhead (everything would rely on dynamic dispatching). That said,
there are certainly situations (e.g., module boundaries) where a
type-erased string could make sense; for such situations, take a look at
any_range within Boost.Range.

- Jeff