type of iterator_facade::value_type
According to iterator_facade doc: typedef remove_const<Value>::type value_type; Why remove_const? This makes it hard to detect if the resulting iterator points to a const value. In order to further adapt such an iterator, I needed to use the reference type instead of the value type to detect constness: typename boost::is_const< typename boost::remove_reference< typename std::iterator_traits<BaseIterator>::reference >::type >::type,
AMDG Neal Becker wrote:
According to iterator_facade doc:
typedef remove_const<Value>::type value_type;
Why remove_const?
This is what the standard does.
This makes it hard to detect if the resulting iterator points to a const value.
value_type is intended to give a type that can be used for temporaries, etc. It was not designed as a general purpose type deduction mechanism. For this purpose, reference is better because reference gives the exact type from dereferencing the iterator.
In order to further adapt such an iterator, I needed to use the reference type instead of the value type to detect constness:
typename boost::is_const< typename boost::remove_reference< typename std::iterator_traits<BaseIterator>::reference >::type
::type,
Yes. Although this is insufficient because it doesn't handle proxies or rvalues. In Christ, Steven Watanabe
At Wed, 23 Dec 2009 09:02:11 -0800, Steven Watanabe wrote:
AMDG
Neal Becker wrote:
According to iterator_facade doc:
typedef remove_const<Value>::type value_type;
Why remove_const?
This is what the standard does.
And with good reason: it would be wicked inconvenient if you tried to declare a variable of the value type and then found you couldn't modify it.
This makes it hard to detect if the resulting iterator points to a const value.
value_type is intended to give a type that can be used for temporaries, etc. It was not designed as a general purpose type deduction mechanism.
Exactly.
For this purpose, reference is better because reference gives the exact type from dereferencing the iterator.
In order to further adapt such an iterator, I needed to use the reference type instead of the value type to detect constness:
typename boost::is_const< typename boost::remove_reference< typename std::iterator_traits<BaseIterator>::reference >::type
::type,
Yes. Although this is insufficient because it doesn't handle proxies or rvalues.
Right. Why are you trying to detect iterator constness? It's hard for me to imagine a good use for that. -- Dave Abrahams Meet me at BoostCon: http://www.boostcon.com BoostPro Computing http://www.boostpro.com
participants (3)
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David Abrahams -
Neal Becker -
Steven Watanabe