Use static_assert to check types passed to macro

Question

I unfortunately have several macros left over from the original version of my library that employed some pretty crazy C. In particular, I have a series of macros that expect certain types to be passed to them. Is it possible to do something along the lines of:

static_assert(decltype(retval) == bool);

And how? Are there any clever alternatives?

Yes I'm aware macros are bad. I'm aware C++ is not C, etc.

Update0

Here is some related code, and the source file. Suggestions are welcome. The original question remains the same.

Answer 1

Most macros can be replaced with inline functions and/or templates. As a case in point, the overly clever argument-size-checking Posix isnan macro is a template in C++0x. Oh,bad example, but you get the idea.

The main exceptions to that rule are macros that essentially implement higher level language features. For example, smarter exception handling, or covariance, or a parameterized set of declarations.

In some cases the macros that can't be reasonable expressed as inline functions or templates, can be replaced with a smarter kind of preprocessing, namely code generation. Then you have a script somewhere that generates the necessary code. For example, it's possible to do options classes in pure C++ with macros and templates, but it's hairy, and as an easier-to-grok and perhaps more maintainable alternative one might use a script that generates the requisite classes, at the cost of extra build steps and dealing with multiple languages.

Cheers & hth.,

Answer 2

It appears you need decltype because you've got an expression, but want to verify a type. There are already enough ways to do that now (C++03). For instance, to check a bool

inline void mustBeBool(bool) { }
template<typename T> inline void mustBeBool(T t) { & (&t); } // Takes address of rvalue (&t)

// Use:
#define DifficultMacro(B) do { mustBeBool(B); foo(B); } while (false)

Answer 3

I found this to be the cleanest, using @UncleBens suggestion:

static_assert(std::is_same<decltype(retval), bool>::value, "retval must be bool");