On Sunday, 11 September 2016 at 12:02:29 UTC, Ethan Watson wrote:
On Sunday, 11 September 2016 at 07:19:54 UTC, John wrote:
You can't really take one sentence out of context, I didn't
say it in the sense that it was completely broken to the point
of being useless.
There's nothing out of context about it. Would it have made you
feel better had I quoted your entire message knowing that I
wouldn't have changed a word of the response?
But if that's how you want to play.
Your comment was out of place, saying properties don't need to be
changed is like saying @property shouldn't even be a D feature
cause you can create the same functional program in C++, which
does not have the property feature. You also made a reference to
C#, which doesn't even allow you take address of So I don't know
what you mean by that's how I want to play, when you instigated
said argument.
The part I'm asking to be changed, you probably didn't even
ever use. C# is a managed language, I don't think you can even
take the pointer of anything unless you enable the unsafe
switch.
You're not showing a good grasp at all as to what a property
is. In C# and in D, a property has *never* guaranteed the
existence of a variable. In both cases, they allow syntactic
sugar for letting the getter/setter pattern established by C++
look like variables.
This is important.
No, really.
Take std.bitmanip for an example of what I was talking about.
It autogenerates properties for a bitfield. The types each
property returns and lets you set are not at all indicative of
the datatype underneath as it's literally just a bunch of bits.
The property functions transform the data types given/return
to/from a bitfield. What exactly do you suggest &property
return if it was to return a char starting at bit 13 of a
bitfield?
It's not really that important. What it allows is returning
references. You can make a comparison to any other language that
has properties it doesn't really matter. This is how D was
implemented. If they wanted to be like every other language then
it shouldn't have been allowed to even return a reference. But it
is does, that's how it's implemented and odds are it probably
won't change now to not allow it. D also has the "&" implemented,
what I am discussing is whether it was implemented correctly or
not. Honestly it is no implemented correctly. To the point I
would actually rather they remove the functionality so that you
can't take the address of a property. If they are not willing to
change it to function in a different way.
This has been brought up by someone else. I honestly don't
understand why it's such a hard concept. Maybe you don't come
from C++ and thus don't use a language that provides a way to
take the address of things. That's why it keeps being brought up.
Anyways a bitfield can't actually represent a single, there's no
type for a bit. The smallest type is a byte, which is 8 bits. So
even if it wasn't a property there's no way you can take the
address of a bit. So that's the first issue, you are trying to
use an example that doesn't make sense even outside the concept
of properties. The second issue is, this is defined behavior. You
can't take the address of a rvalue, there's an ideone link in my
previous post show this if you missed it. So taking the address
of a property would return an error if it didn't return a
reference.
But we can go one further. __traits( allMembers, Type ) and
__traits( getMember, Type ). Let's say you're writing an
auto-serialisation library (or take std.json as an example).
Assuming a property is a stand-in for another variable then
what happens there when you're checking for the type of a
member is the delegate type, and later on you'll get the actual
variable. Now change it so that the type of a property returns
the actual type. Now you're serialising a piece of data twice.
But what if our @property function increments another variable
inside a class whenever you access it? That's pretty dangerous
if you start treating the property as an actual type instead of
a function/delegate.
Well that's how it is currently implemented actually.
struct S
{
@property int prop() { return 0; }
}
writeln(typeof(S.prop).stringof) // prints "int", not
"delegate"
I'm only talking about taking the address of a property. That
does no way infer that there shouldn't be some way to identify
that it is a property at compile time. The way you should check
if a member is a property shouldn't be by taking the address of
it. That's not as clear as having a trait or other implementation
such that you could do "isProperty". That is much more clearer.
If the only way to identify a property is by checking the
typeof() a member for when you take it's address, then that's a
hack and a better way to identify a property should be
implemented.
Thus, your example:
&t.x // returns "ref int delegate()"
&t.x() // ok returns "int*", but defeats purpose of
@property
&(t.j = 10) // shouldn't this return "ref int
delegate(int)" ?
First one I'd expect. Second one I'd expect. Third one I'd
expect results in int*. You're getting the address of the
results of the assign operation. Look at it this way: int val =
(t.j = 10); You'd expect val and t.j to be 10, right? So why do
you expect to get a ref int delegate(int) just because you ask
for the address of it?
Well I put that there more satirically, as as far as I am aware
there is no way to get the delegate for the setter. Getting the
delegate from t.x would make as much sense as it does for that
setter function.
