On Sun, 24 Apr 2011 07:29:22 -0400, Jacob Carlborg <[email protected]> wrote:
On 24 apr 2011, at 01:27, Jonathan M Davis wrote:
On 22 apr 2011, at 00:28, Jonathan M Davis wrote:
Actually, setters _should_ return void. The chaining should be done by
calling both the getter and setter functions. The other options is a
property function which takes nothing but returns a ref. In either
case,
the chaining would work.
Wouldn't this require some form of property rewriting?
Hmmm. Yes it would, which I was thinking was what properties were doing
anyway, but now that I think on it, I'm not sure they do. The getter
certainly
doesn't, but I don't know about the setter. So, I'm not quite sure what
the
compiler is doing right now, but calling both the getter and setter for
chained assignment would require a lowering.
I'm pretty sure it doesn't do any property rewriting. There's also this
problem (that also C# has) that also has been discussed before:
foo.bar.value = 3;
"foo" is a struct or an object. "bar" is a getter property which returns
an object and "value" is setter property that sets a value. If you have
some kind validation in a "bar" setter property it will be bypassed.
This can be fixed with property rewriting. BTW, I pretty sure there's an
issue in bugzilla about this.
Yes, there is a a bug about it, but it doesn't occur when 'bar' is an
object/ref T, it occurs when 'bar' is a struct/value type. It happens
because 'a.b.c = 5' gets rewritten into 'auto temp = a.b; temp.c = 5;' If
b/temp is a reference type, then that store is meaningful. However, if
b/temp is a struct/value type, then assignment is made to a local copy and
is lost. I believe the proposed fix would is: 'a.b.c = 5' => 'auto t =
a.b; t.c = 5; a.b = t;', with greater number of temporaries as the number
of references lengthens.
Then again, now that I think of it, if you require both the getter and
setter
for chained assignment, chained assignment won't work for write-only
properties. So, I don't know what the solution should be. It was my
understanding that a function could _be_ a setter if it returned
anything. It
had to take a single value and return nothing (or take two values where
the
first was an array and you were calling it using the array's member
function
call syntax). And with that being the case, you _must_ use the getter to
generate chained assignments.
Can't that be a requirement, to have a getter, to be able to do chained
assignment. How often do you actually provide only a setter without a
getter?
I've written and used setters that don't have a getter before, but they
are not a common use case. But I don't believe you could have such a
method be anything other than the last one in the chain. i.e. given 'a.b.c
= 5', c doesn't need to have a getter, but b definitely does. (Also,
'a.b.c += 5' would require c to have a getter)
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