Re: [boost] [range] boost::end("hello") is sub-optimal

From: Eric Niebler (eric_at_[hidden])
Date: 2006-01-02 00:18:05

MB wrote:
> Eric Niebler wrote:
> 
>>There is a bug in Boost.Range that is causing boost::end() to execute a 
>>slower code path when called with a string literal. The type of "hello" 
>>is char const [6], and end() should be O(1). Indeed, Boost.Range has 
>>code to handle just this case, but it never gets called. The problem is 
>>the way overload resolution happens between these two functions
>>
>>    template< typename T, std::size_t sz >
>>    const T* boost_range_end( const T (&array)[sz] )
>>
>>    const char* boost_range_end( const char* s )
>>
>>The first is O(1) and the second is O(N) becuase it calls strlen. But 
>>the second will always be chosen because non-templates are preferred 
>>over templates.
>>
> 
> 
> I guess that is intentional.
> See: boost::end("hello\0secret")

I don't think it's intentional. There is explicit code for the handling 
of arrays of char that is never getting called. Presumably, it's not 
there just because Thorsten likes to type. :-) Your point is valid, 
though -- it would lead to inconsistent behavior.

We'll have to wait for Thorsten to answer. This may all be moot. I 
recall Thorsten agreeing to remove direct support for null-terminated 
strings from Boost.Range and adding a utility for creating a range from 
a char*.

> BTW, '#define foreach BOOST_FOREACH' causes name conflict with Boost.Foreach. :-)

Yup, fixed. Thanks.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com