• Nick (4/8) May 16 2021 Is this warning still valid? The standard library appears to
• Adam D. Ruppe (20/21) May 16 2021 The @property thing doesn't do much. All it does is change
• Paul Backus (10/16) May 16 2021 It's not required:
• Steven Schveighoffer (5/11) May 17 2021 It used to be required, but we removed that requirement a long time ago....
• Adam D. Ruppe (5/7) May 17 2021 yeah i remember ElementType required it last time i checked but
• Nick (10/31) May 17 2021 Thanks for the detailed explanation. I guess the wording of the

Nick <my_dlang bestmail.us> writes:

The [Property 
Functions](https://dlang.org/spec/function.html#property-functions)
documentation reads:

 WARNING: The definition and usefulness of property functions is 
 being reviewed, and the implementation is currently incomplete. 
 Using property functions is not recommended until the 
 definition is more certain and implementation more mature.

Is this warning still valid? The standard library appears to 
extensively use property functions.

Adam D. Ruppe <destructionator gmail.com> writes:

On Sunday, 16 May 2021 at 15:12:25 UTC, Nick wrote:
 Is this warning still valid?

The  property thing doesn't do much. All it does is change 
typeof(a.prop) from function over to the return value of the 
function. (Which actually makes it required for the range empty 
and front things!)

But since it doesn't do much it makes it very easy to misuse it 
too - putting it somewhere where it doesn't belong will NOT cause 
the compiler to issue an error.

So that's why it is warned: the current behavior is extremely 
minimal and if that expands and you misused it, you'll see broken 
code down the line.

But on the other hand,  property has been a do-nothing for a 
decade now, so I wouldn't expect that to change any time soon.

My general rule is to put it on something that should be 
replaceable with a public data member. If you can't do that, 
don't make it  property. In particular, do NOT put it on 
something for the sole reason of not using () on the call. 
 property is not really related to parenthesis syntax. Only use 
it when it is specifically meant to be replaceable with a public 
member.

Paul Backus <snarwin gmail.com> writes:

On Sunday, 16 May 2021 at 15:47:55 UTC, Adam D. Ruppe wrote:
 On Sunday, 16 May 2021 at 15:12:25 UTC, Nick wrote:
 Is this warning still valid?

 The  property thing doesn't do much. All it does is change 
 typeof(a.prop) from function over to the return value of the 
 function. (Which actually makes it required for the range empty 
 and front things!)

It's not required:

     struct Example
     {
         int front() { return 42; }
         bool empty() { return false; }
         void popFront() {}
     }

     import std.range;
     static assert(isInputRange!Example);

Steven Schveighoffer <schveiguy gmail.com> writes:

On 5/16/21 11:47 AM, Adam D. Ruppe wrote:
 On Sunday, 16 May 2021 at 15:12:25 UTC, Nick wrote:
 Is this warning still valid?

 
 The  property thing doesn't do much. All it does is change 
 typeof(a.prop) from function over to the return value of the function. 
 (Which actually makes it required for the range empty and front things!)

It used to be required, but we removed that requirement a long time ago. 
It was inconsistently applied (some features required  property, and 
some did not).

-Steve

Adam D. Ruppe <destructionator gmail.com> writes:

On Monday, 17 May 2021 at 14:56:21 UTC, Steven Schveighoffer 
wrote:
 It used to be required, but we removed that requirement a long 
 time ago.

yeah i remember ElementType required it last time i checked but 
that was a while ago

indeed it is all fixed now

Nick <my_dlang bestmail.us> writes:

On Sunday, 16 May 2021 at 15:47:55 UTC, Adam D. Ruppe wrote:
 On Sunday, 16 May 2021 at 15:12:25 UTC, Nick wrote:
 Is this warning still valid?

 The  property thing doesn't do much. All it does is change 
 typeof(a.prop) from function over to the return value of the 
 function. (Which actually makes it required for the range empty 
 and front things!)

 But since it doesn't do much it makes it very easy to misuse it 
 too - putting it somewhere where it doesn't belong will NOT 
 cause the compiler to issue an error.

 So that's why it is warned: the current behavior is extremely 
 minimal and if that expands and you misused it, you'll see 
 broken code down the line.

 But on the other hand,  property has been a do-nothing for a 
 decade now, so I wouldn't expect that to change any time soon.

 My general rule is to put it on something that should be 
 replaceable with a public data member. If you can't do that, 
 don't make it  property. In particular, do NOT put it on 
 something for the sole reason of not using () on the call. 
  property is not really related to parenthesis syntax. Only use 
 it when it is specifically meant to be replaceable with a 
 public member.

Thanks for the detailed explanation. I guess the wording of the 
warning seems strange to me, in that it recommends not to use 
property functions; but, in actuality (and regardless?), these 
functions are used a lot (even in the standard library; at least 
from what I've seen). Also, although this warning is delivered, 
there is nothing in the documentation that explicitly addresses a 
concrete downside (or recommended limitation) to using them. 
However, your explanation does provide some context to this 
warning.