On Wed, 23 Feb 2011 14:28:01 -0500, %u <wfunct...@hotmail.com> wrote:
No. pure is what we want. Changing it would break code and contradict
TDPL (though the
addition of weakly pure isn't in TDPL). Strongly pure functions are
essentially what you'd
expect from pure. Weakly pure functions aren't, but they're necessary to
make pure very
useful, and there's no real benefit in using a new keyword or attribute
to mark them. pure is
the word used because we're modeling the idea that multiple calls to the
same function with
the same parameters have the same result - which is indeed the case with
strongly pure
functions. The funny case is weakly pure, but it's _not_ optimized out,
and it's necessary for
pure to be useful. You can clearly see whether a function is weakly or
strongly pure by
looking at its signature, so I really don't think that it's an issue.
You keep on mentioning that weakly pure "is necessary for pure to be
useful", but the problem
is, even if something looks like a duck and walks like a duck, that
doesn't mean it's a duck!
Just because __declspec(noalias) _appears_ to mean the same thing as
pure from the outside
perspective that doesn't bother to peek too much into things doesn't
mean that it's the same
thing (it obviously isn't).
Jonathan's point is that pure is what we say it is, because that's the
definition of the language. If you want Microsoft's version of pure, use
Microsoft's language/compiler. D's definition of pure is what we said it
is.
Note that weak pure does fit within the definition of "having no side
effects." That is, it cannot alter things it is not passed via parameters.
You're mentioning yourself that "weakly pure" isn't in the language
specs... and if DMD is
supposed to be a D compiler, shouldn't it actually follow the exact
spec? (If "weakly pure"
was actually intentional, then shouldn't it actually _be_ in the spec?
Otherwise, the compiler
is clearly contradicting TDPL about a fundamental CS concept, isn't it?)
Strong pure and weak pure functions have no visible difference, and one
can be used wherever the other is used. The difference between strong and
weak pure is only how the compiler deals with them. So from a user
perspective, strong and weak pure are the same, both are pure functions
and have the same restrictions.
-Steve
