TITLE: New mutable keyword


PROBLEM: jamesc@dev.state.com.au (James Cribb)

In situations where you have a variable declared as const but need to
change it (for some good reason of course), you can `cast away const'.


RESPONSE: maxtal@physics.su.OZ.AU (John Max Skaller), 8 Aug 93


	WARNING! This is not true anymore! For example:

	f(){
		const int i=2;
		(int&)i = 1; // error
	};

	[ This is actually accepted by the ObjectCenter compiler. -adc ]

This is an error, and has been for some time. However 

	f() {
		const complex c(1,1);
		(complex&)c = complex(2,2); // was OK, now not OK
	}

This used to be fine because 'complex' has a constructor. 
Since Munich, this is an error. Violating the constness of
a variable is now not allowed. 

The change came about with the introduction of 'mutable'
members:

	class X {
		int i;
		mutable int j;
	};

	const X x = {1,2};
	x.j=3; // fine: mutable
	x.i=6; // error

[...]