On Tuesday, 30 October 2012 at 02:27:30 UTC, Mehrdad wrote:
I understand the problem, but it doesn't seem related to
structs at all.
Any two attempts to compare two default-valued floats will
fail, irrespective of whether or not they're inside structs.
True at the level of float by float comparisons, but not
necessarilly true when struct by struct bit pattern compares are
done.
My original understandiong of the struct type in D, is that it is
defined as a POD which means == (without override) is done as a
simple bit pattern compare, rather than doing a value by value
compare of member data types. If this is the case, then two
structs with default valued equivalent float types should compare
equal, even though a value by value compare would compare not
equal.
TDPL clearly states that each of the struct's members are
supposed to
be checked for equality (see section 7.1.5.2, p. 258 - 259).
So I guess that the POD definition of struct was changed at some
point?
If so, then how are value by value compares performed when unions
are involved? What about when there are member pointers, and
other structures that cannot be compared in a meaningful way by
default?
I guess the question is if the bit pattern comparision of structs
has sufficient justification to be worth having as the default
behaviour, or if there is more value attempting a value by value
comparision, even though in many situations it may be pointless
to attempt either strategy.
In my experience, I cannot recall doing very many direct struct
comparisons either as a complete value by value compare or as a
full bit pattern compare, I just never found it to be all that
useful, no matter, I can try and imagine both strategies being
useful in some situations.
With operator overloading you can have both strategies, but only
if bit pattern compare is the default stategy, plus with
overloading, compare can do exactly what you want to make sense
out of unions and pointers, etc. So we should be good as is. I
would expect that most times no one compares structs fully by
value or by bit pattern anyway, to do so very often is difficult
for me to imagine, but I could be wrong.
--rt
