What is the case against a struct post-blit default constructor?

[Jonathan M Davis]

On Thursday, October 11, 2012 13:06:34 Walter Bright wrote:
> On 10/11/2012 10:23 AM, Jonathan M Davis wrote:
> > but there _are_ cases
> > where you can't have an invariant because of it.
> 
> Except that you could write the invariant to be inclusive of the .init
> state.

Which would completely defeat the purpose of the invariant in many cases. The 
point is that it is invalid to use the init value. You can pass it around and 
set stuff to it and whatnot, but actually calling functions on it would be 
invalid, because its init state isn't valid. SysTime is a prime example of 
this, because it requires a valid TimeZone object, but its init value can't 
have one, because TimeZone is a class. So ideally, it would have an invariant 
which asserts that its TimeZone is non-null, but it can't have that, because 
opAssign unfortunately checks the invariant before it's called (which makes no 
sense to me - why would the state of the object prior to assignment matter? 
you're replacing it), so assigning a valid value to a default-initialized 
SysTime would fail the invariant.

- Jonathan M Davis