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Implemented BOOST_TYPEOF_NESTED_TYPEDEF.

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This macro works around known bugs in VC7.1 and VC8.0 concerning the use of BOOST_TYPEOF inside templates. It also eliminates the limitation imposed by BOOST_TYPEOF_LIMIT_SIZE.


[SVN r33355]
This commit is contained in:
Peder Holt
2006-03-16 17:10:19 +00:00
parent e2d492bb49
commit dbfa74603c
12 changed files with 198 additions and 31 deletions
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doc/typeof.qbk
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@@ -578,7 +578,7 @@ but removes the top-level qualifiers, `const&`
BOOST_TYPEOF_TPL(expr)
[variablelist Arguments
[[expr][a valid c++ expression that has a type]]
[[expr][a valid c++ expression that can be converted to const T&]]
]
[h4 Remarks]
@@ -602,6 +602,48 @@ which takes care of `typename` inside the `typeof` expression.
[endsect]
[section:typo TYPEOF_NESTED_TYPEDEF, TYPEOF_NESTED_TYPEDEF_TPL]
The `TYPEOF_NESTED_TYPEDEF` macro works in much the same way as the 'TYPEOF' macro does, but
workarounds several compiler deficiencies.
[h4 Usage]
BOOST_TYPEOF_NESTED_TYPEDEF(name,expr)
BOOST_TYPEOF_NESTED_TYPEDEF_TPL(name,expr)
[variablelist Arguments
[[name][a valid identifier to nest the typeof operation inside]
[expr][a valid c++ expression that can be converted to const T&]]
]
[h4 Remarks]
'typeof_nested_typedef' nests the 'typeof' operation inside a struct. By doing this, the 'typeof' operation
can be split into two steps, deconfusing several compilers (notably VC7.1 and VC8.0) on the way.
This also removes the limitation imposed by `BOOST_TYPEOF_LIMIT_SIZE` and allows you to use 'typeof' on much
larger expressions.
If you want to use `typeof_nested_typedef` in a template-context, use `BOOST_TYPEOF_NESTED_TYPEDEF_TPL(name,expr)`,
which takes care of `typename` inside the `typeof` expression.
[h4 Sample Code]
template<typename A, typename B>
struct result_of_conditional
{
BOOST_TYPEOF_NESTED_TYPEDEF_TPL(nested,true?A():B());
typedef typename nested::type type;
};
template<typename A, typename B>
result_of_conditional<A, B>::type min(const A& a,const B& b)
{
return a < b ? a : b;
}
[endsect]
[endsect]
[section:other Other considerations and tips]