Is there anything wrong with a union having one or more methods? Or anything to watch out for? (I can see constructors/destructors being problematic for schizophrenic reasons)
A:
How could you possibly implement such a thing? Here's a pointer to a union, hope you don't mind that you have no idea which variables are safe to use and which aren't.
Unions are a dead language feature really anyway- they've been totally superseded by library-based methods like boost::variant or boost::any. Kind of similar to the void* and functional macros - they're very rarely useful in C++ compared to other options.
DeadMG
2010-10-29 22:13:41
Don't forget the embedded world. Sometimes things aren't 100% typesafe.
Jason S
2010-10-29 23:30:45
@Jason: How does being embedded change anything? Either you know what type it is, so use a regular variable, you know all the types are related, so use polymorphism, or you need to know what type it is before you can do anything.
DeadMG
2010-10-29 23:41:49
@DeadMG: Embedded doesn't change anything about the language per se, but it does place limits on dynamic memory allocation and polymorphism ( it's both types.
Jason S
2010-10-29 23:59:13
One of C++'s strengths is that it does not forget that it is actually running on real world hardware, and unions are one of the tools that can greatly simplify this work.
Rob K
2010-10-30 02:38:54
+6
A:
From the C++03 & C++0x (Draft N3092) standards:
9.5 Unions
A union can have member functions (including constructors and destructors), but not virtual (10.3) functions. A union shall not have base classes. A union shall not be used as a base class.shall not be used as a base class.
As long as initializing the union using the aggregate initializer syntax (U u = { 42 };) or setting a member afterwards (U u; u.i = 42;) is not "problematic" initializing it using a constructor (U u( 42 );) is not "problematic" either.
The only "catch" is that you cannot use the aggregate initializer syntax for a union that has a user defined constructor.
Eugen Constantin Dinca
2010-10-29 22:21:12
unions can have constructors? then when is/isn't construction a problem?
Jason S
2010-10-30 14:49:20