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Utility::Debug: add std::ostream output operator call converter #88

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Utility::Debug: add std::ostream output operator call converter #88

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6964c21
Utility::Debug: DebugOstreamFallback enable if has ostream operator
rune-scape Jan 24, 2020
bcc6544
Merge https://github.com/mosra/corrade into pr88
rune-scape Jan 27, 2020
dfa849b
Move DeclareLvalueReference to TypeTraits.h
rune-scape Jan 28, 2020
8b1e935
Utility::Debug: add HasDebugStreamOperator check to DebugOstreamFallback
rune-scape Jan 29, 2020
cf3f6fd
Utility::Debug: added std::ostream output operator call converter.
rune-scape Jan 29, 2020
8b048e6
Utility: doc++
rune-scape Jan 29, 2020
05cfb24
Utility::Debug: OstreamDebug::operator<< is now in its own namespace
rune-scape Feb 2, 2020
3b75172
Utility::Debug: more docs
rune-scape Feb 2, 2020
be5dfa9
Utility: snippet had narrowing conversion
rune-scape Feb 2, 2020
9abf7c3
Utility: DebugTest.cpp: corrected sourceLocation test
rune-scape Feb 2, 2020
b3129ed
Utility: whitespace at EOL.
mosra Feb 5, 2020
07dad62
Utility: this is how it is expected to work.
mosra Feb 5, 2020
ccb7bcd
Utility: eureka!
mosra Feb 5, 2020
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25 changes: 24 additions & 1 deletion src/Corrade/Utility/DebugStl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -103,9 +103,32 @@ template<class ...Args> Debug& operator<<(Debug& debug, const std::tuple<Args...

namespace Implementation {

template<typename T>
typename std::add_lvalue_reference<T>::type declare_lvalue_reference() noexcept;
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template<typename T>
struct has_ostream_operator {
private:
template<typename C>
static constexpr auto check(C *) ->
typename std::is_same<
decltype(declare_lvalue_reference<std::ostream>() << std::declval<C>()),
std::add_lvalue_reference<std::ostream>::type
>::type;

template<typename>
static constexpr std::false_type check(...);

public:
static constexpr bool value = decltype(check<T>(nullptr))::value;
};

@mosra mosra Jan 26, 2020

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There's a (admittedly weirdly named) CORRADE_HAS_TYPE(className, typeExpression) macro that already contains the above functionality, but your variant seems to be a lot simpler than what I stole from somewhere back in the day :) If I fix the macro to have the second parameter variadic (so the comma doesn't break it), I think we could then reduce the above to be just this (containing the potentially hard-to-understand template magic in a single place):

CORRADE_HAS_TYPE(HasOstreamOperator, typename std::is_same<
    decltype(declareLvalueReference<std::ostream>() << std::declval<C>()),
    std::add_lvalue_reference<std::ostream>::type
>::type)

(Also adapting the naming to what Corrade uses for type traits.) I hope I didn't overlook something that would make this impossible tho.

@mosra mosra Jan 26, 2020

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CORRADE_HAS_TYPE() is fixed to allow this in 8d4eb5b, and I think it would work with a minor change:

CORRADE_HAS_TYPE(HasOstreamOperator, typename std::enable_if<std::is_same<
    decltype(declareLvalueReference<std::ostream>() << std::declval<C>()),
    std::add_lvalue_reference<std::ostream>::type
>::value>::type)

I assume you have some way to test the infinite recursion already -- can you confirm? :)

@rune-scape rune-scape Jan 28, 2020

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yes! works perfectly. A very useful macro too


/* Used by Debug::operator<<(Implementation::DebugOstreamFallback&&) */
struct DebugOstreamFallback {
template<class T> /*implicit*/ DebugOstreamFallback(const T& t): applier(&DebugOstreamFallback::applyImpl<T>), value(&t) {}
template<
class T,
typename = typename std::enable_if<has_ostream_operator<T>::value>::type
> /*implicit*/ DebugOstreamFallback(const T& t): applier(&DebugOstreamFallback::applyImpl<T>), value(&t) {}

void apply(std::ostream& s) const {
(this->*applier)(s);
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