On Fri, 24 Sep 2010 13:09:05 -0400, Steven Schveighoffer
<schvei...@yahoo.com> wrote:
On Fri, 24 Sep 2010 12:16:23 -0400, Robert Jacques <sandf...@jhu.edu>
wrote:
On Fri, 24 Sep 2010 10:47:16 -0400, Steven Schveighoffer
<schvei...@yahoo.com> wrote:
On Fri, 24 Sep 2010 10:33:10 -0400, Robert Jacques <sandf...@jhu.edu>
wrote:
On Fri, 24 Sep 2010 09:32:40 -0400, Steven Schveighoffer
<schvei...@yahoo.com> wrote:
structs can have value copy semantics. But for a struct that
contains a reference, the references have reference semantics, which
makes the struct a reference type.
A struct is never a reference type. It may have reference semantics,
but this is a high-order feature that is uncheckable by the compiler.
At best the compiler can detect that a struct contains references,
not how those references are exposed/managed by the API.
Containing references means it cannot be cast to immutable, the only
important thing when determining the strength of purity here.
This whole discussion is going nowhere, you haven't made any real
points. Can you think of a case where the compiler would be wrong in
determining purity strength for "value types" as you define them? An
example would be most helpful.
-Steve
I feel like I've upset you and would like to make amends. First, this
discussion was never about the compiler being able to determine purity.
That's easy. The point raised was about whether the programmer could
enforce strong-purity for any strongly-pure fucntion. The answer is
that you can by making all arguments immutable, which is a fairly minor
restriction on the callee. Second, this thread (fiber?), has veered a
little off-topic due to a misunderstanding/debate about value-types vs
value-semantics and reference-types vs reference-semantics. Perhaps
it's because I work with large, 'hybrid' structs a lot, but the
difference between value-type and value-semantics is very large in my
mind. Third, this fiber started, in part, due to a question by
regarding value-types being answered with value-semantics. Forth, I
raised the question regarding value-types in part due to
half-remembered old posts in which value-semantics were discussed but
under the label of value-types, thus causing confusion in my brain. And
because it was late at night, I decided to ask a simple question
instead of testing DMD's current behavior myself. I did end up testing
DMD the next day (and then banging my head on a wall), but by then all
this had started.
You haven't upset me, I just couldn't follow what you were saying :)
When you said "what about value types," I thought it was a suggestion
that value types would make it hard to determine whether a function was
strongly pure or weakly pure, and my interpretation of what "value type"
means sent us off on this tangent.
I think we both agree that the proposed changes by Don will work with
the compiler, and I understand your desire to ensure a function is
strongly-pure, and why the proposal does not give an easy solution to
that.
So no hard feelings, we can move on and forget this whole thread ever
happened :)
-Steve
Agreed :)
