CODEWITHSUNDEEP
c++macrosc++11c-preprocessor
There is nothing we can do
There is nothing we can do

Reputation: 24705

Writing a macro

How I'm suppose to implement a macro that would do something like this:
//pseudocode 

#define CHOOSE(X) if(X) expand to "" and if !X expand to return nullptr;

Edit 

template<class SomePolicy>
struct M
{

template<class Policy = SomePolicy>
typename std::enable_if<IsThrow<Policy>::value,void>::type fnc()
{
}

template<class Policy = SomePolicy>
typename std::enable_if<!IsThrow<Policy>::value,std::nullptr_t>::type fnc()
{
    return nullptr;
}
};

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Upvotes: 0

Views: 228

Answers (4)

Alexey Malistov
Alexey Malistov

Reputation: 27023

Answer to edit section. Use the fact that expression return g(); is valid even if g return void.

template <class T> T GetDefault() { return T(); }
template <> void GetDefault<void>() {  } // special case for void

and use

return GetDefault<void>();

or 

return GetDefault<std::nullptr_t>();

Upvotes: 2

Viktor Sehr
Viktor Sehr

Reputation: 13119

#define CHOOSE(X) (return(X)?"":nullptr)

Upvotes: 0

Steve Townsend
Steve Townsend

Reputation: 54178

Don't use a macro, use an inline function. I am not sure what it would return in this case but that's an issue either way.

Upvotes: 1

siukurnin
siukurnin

Reputation: 2902

You're not supposed to implement macros if you have C++ !

What do you want to do exactly ???

Upvotes: 1

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