Default-constructed function_output_iterator with function pointers is unusable
and previously would have contained an uninitialized function pointer.
Disable the default constructor using SFINAE to prevent misuse.
Also reformat code.
Use EBO to minimize wasted storage space if the predicate is an empty class.
Disable default constructing non-class predicates using SFINAE instead
of a static_assert. This will help type traits like is_constructible,
when applied to the iterator type.
The new eval_if_default helper replaces both ia_dflt_help and
ia_eval_if_default helpers. Additionally, added a new if_default
helper, which expands to the type or the default parameter directly.
The new helpers are placed in separate headers which can be used
without the iterator_adaptor template.
The new min_category is similar to minimum_category but accepts variable
number of iterator categories on input instead of just two, and also does
not depend on Boost.MPL for lambda placeholders. The existing minimum_category
trait has been reimplemented in terms of min_category and deprecated.
We don't yet emit deprecation warnings as there is still code that uses
the old trait which we first need to update. Eventually, minimum_category
will emit warnings and will be removed.
Performance improvement: Add move semantics to by-value parameters (iterator and predicate), to eliminate the cost of copy-construction. Both the Predicate (Normally a std::function, or lambda), and custom iterators can have state, which can be expensive to copy. Profiler identified this as a bottleneck while using boost::adaptors::filtered.
The MPL version is slower to compile and `BOOST_STATIC_ASSERT` is
already used in some places. So unify that.
This also fixes `Wzero-as-null-pointer-constant` warnings, see https://github.com/boostorg/mpl/pull/75
The recent commit 5777e9944b broke code such as
(*it++).foo(), where the result of dereferencing would be convertible to
the value type but did not provide the members of the value type. To mitigate
this, return a reference to the value instead of a proxy object. This will only
work for non-writable iterators (and it didn't work for writable iterators
before either) because in that case a proxy is needed to be able to intercept
operator=.
Also fix a similar issue with (it++)->foo() by adding operator-> overloads
to the post-increment result proxies.
Added tests for the fixes.
This allows expressions such as `Iterator it2(it1++)` to compile.
Additionally separated operations that are allowed on the result of
dereferencing the proxy to a separate set of proxies to make the allowed
set of expressions more strict and unambiguous. In particular, it means
`it++` cannot be converted to value type and `*it++` cannot be converted
to the iterator type anymore. Also, make sure `*it1++ = *it2++` works
as expexted by explicitly converting the proxy to the value type on
assignment.
Fixes https://github.com/boostorg/iterator/issues/75.
This fixes incorrect final iterator type being used in iterator_facade, which
results in an internal base class being returned from various facade methods.
Reported in https://github.com/boostorg/iterator/issues/75.
