On Sunday, September 09, 2012 17:09:23 Namespace wrote: > On Saturday, 8 September 2012 at 23:18:14 UTC, Timon Gehr wrote: > > On 09/09/2012 01:16 AM, Namespace wrote: > >> Why fail this code? > >> without "const" on "Name" it works fine. > >> > >> http://dpaste.dzfl.pl/9fa0986a > > > > const fields cannot be written to. This includes the case when > > the > > entire struct is written to at once. > > But i assign the const attribute in the ctor. So this behaviour > doesn't make any sense...
const member variables can be initialized but never assigned to. They're either directly initialized or initialized by the constructor. After that (including later in the constructor), you can't change them. This also makes the default assignment operator illegal. You could overload it, and as long as it doesn't touch any of the const member variables, it would work, but the const member variable is stuck as it is, and anything trying to mutate is illegal. Really, having const member variables is a _bad_ idea IMHO - particularly for structs. At least with a class, if you try and replace the object's value, you generally just allocate a new object and assign it to the reference. But with structs, which are almost always on the stack, you can't assign to it anymore once it has a const member variable, which causes all kinds of annoying problems. You're just better off if you never declare structs with const or immutable member variables. - Jonathan M Davis
