On 2019-05-20 11:25, Giuseppe D'Angelo via Development wrote:
Hi,
Il 19/05/19 18:54, Thiago Macieira ha scritto:
But I think all Qt classes should go beyond that, unless they have
VERY good
reasons not to do so (and document so). The moved-from object should
also be
in a valid state so all the accessor and mutation API in the class can
operate
in the object without ill effects. What they actually do, we can't
tell, since
the initial state is unknowable. So apply the principle of GIGO.
So basically the same stance as the Standard Library? One should be
able to invoke any function without preconditions on a moved-from
object?
Except that the standard library has an easy way of implementing that,
since there're no PIMPLs. For a PIMPLed class, it means that the move
constructor either must allocate memory or that each and every PIMPLed
value class needs to have a static unsharable null instance. This is
relatively easy for some, but try that for QBrush. Or we litter all
member functions with nullptr checks.
I agree that a moved-from object should be in the same state as a
default-constructed one. I disagree with that that state must always be
a valid value of the class. I agree with Stepanov that the default
constructor should be establishing the partially-formed state, ie, only
destruction and assignment are valid. It _can_ do more, but only if it
stays noexcept.
Or maybe we don't disagree at all and Thiago would accept allocating
memory (or, by extension, anything that's noexcept(false)) as a very
good reason to have a nullptr d?
Thanks,
Marc
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