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Because of the errors in MSVC with fowarding and static_casting arrays it was decided to drop minor optimization and do not perfect forward source types in try_lexical_convert

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This commit is contained in:
Antony Polukhin
2014-02-06 11:22:40 +04:00
parent 5a757dcece
commit 90b4286753
2 changed files with 8 additions and 27 deletions
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13
doc/lexical_cast.qbk
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@@ -72,7 +72,7 @@ Library features defined in [@boost:boost/lexical_cast.hpp boost/lexical_cast.hp
namespace conversion
{
template<typename Target, typename Source>
bool try_lexical_convert(Source&& arg, Target& result);
bool try_lexical_convert(const Source& arg, Target& result);
template <typename AnyCharacterType, typename Target>
bool try_lexical_convert(const AnyCharacterType* chars, std::size_t count, Target& result);
@@ -134,11 +134,11 @@ Exception used to indicate runtime lexical_cast failure.
[section try_lexical_convert]
`boost::lexical_cast` remains the main interface for lexical conversions. It must be used by default in most cases. However
some developers wish to make their own conversion functions, reusing all the optimizations of `boost::lexical_cast`. That's
where the `boost::conversion::try_lexical_convert` function steps in.
some developers wish to make their own conversion functions, reusing all the optimizations of the `boost::lexical_cast`.
That's where the `boost::conversion::try_lexical_convert` function steps in.
`try_lexical_convert` returns `true` if conversion succeeded, otherwise returns `false`. If conversion failed and `false` was returned,
state of `result` output variable is undefined.
`try_lexical_convert` returns `true` if conversion succeeded, otherwise returns `false`. If conversion
failed and `false` was returned, state of `result` output variable is undefined.
Actually, `boost::lexical_cast` is implemented using `try_lexical_convert`:
``
@@ -154,8 +154,7 @@ Actually, `boost::lexical_cast` is implemented using `try_lexical_convert`:
}
``
`try_lexical_convert` relaxes the requirements for `Target` type. `Target` must not be CopyConstructible or DefaultConstructible.
`try_lexical_convert` relaxes the CopyConstructible and DefaultConstructible requirements for `Target` type.
Following requirements for `Target` and `Source` remain:
* Source must be OutputStreamable, meaning that an `operator<<` is defined that takes a `std::ostream` or `std::wostream` object on the left hand side and an instance of the argument type on the right.

22
include/boost/lexical_cast.hpp
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@@ -2077,9 +2077,6 @@ namespace boost {
i_interpreter_type i_interpreter;
// Disabling ADL, by directly specifying operators.
//
// For compilers with perfect forwarding `static_cast<forward_type>(arg)` is
// eqaul to `std::forward<T>(arg)`.
if (!(i_interpreter.operator <<(arg)))
return false;
@@ -2252,25 +2249,10 @@ namespace boost {
namespace conversion { namespace detail {
// MSVC fail to forward an array (DevDiv#555157 "SILENT BAD CODEGEN triggered by perfect forwarding",
// fixed in 2013 RTM).
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES) && (!defined(BOOST_MSVC) || BOOST_MSVC >= 1800)
template <typename Target, typename Source>
inline bool try_lexical_convert(Source&& arg, Target& result)
{
typedef BOOST_DEDUCED_TYPENAME boost::remove_const<
BOOST_DEDUCED_TYPENAME boost::remove_reference<Source>::type
>::type no_cr_source_t;
typedef Source&& forward_type;
#else
template <typename Target, typename Source>
inline bool try_lexical_convert(const Source& arg, Target& result)
{
typedef Source no_cr_source_t;
typedef const Source& forward_type;
#endif
typedef BOOST_DEDUCED_TYPENAME boost::detail::array_to_pointer_decay<no_cr_source_t>::type src;
typedef BOOST_DEDUCED_TYPENAME boost::detail::array_to_pointer_decay<Source>::type src;
typedef BOOST_DEDUCED_TYPENAME boost::type_traits::ice_or<
boost::detail::is_xchar_to_xchar<Target, src >::value,
@@ -2302,7 +2284,7 @@ namespace boost {
typedef BOOST_DEDUCED_TYPENAME caster_type_lazy::type caster_type;
return caster_type::try_convert(static_cast<forward_type>(arg), result);
return caster_type::try_convert(arg, result);
}
template <typename Target, typename CharacterT>