Discussion Thread: DIP 1043--Shortened Method Syntax--Community Review Round 1

[Timon Gehr]

On 04.02.22 18:18, Tejas wrote:
> On Friday, 4 February 2022 at 14:46:39 UTC, Paul Backus wrote:
>> On Friday, 4 February 2022 at 12:40:32 UTC, max haughton wrote:
>>> On Friday, 4 February 2022 at 11:21:48 UTC, Elronnd wrote:
>>>> It would be nice to permit something like this:
>>>>
>>>> struct Foo {
>>>>     this(int x, string y) { ... }
>>>>     this(string y) => this(0, y);
>>>> }
>>>>
>>>> Currently this fails because constructors are not allowed to return 
>>>> anything.  But that should not be part of this DIP, probably.
>>>
>>> The implementation as done by Adam is done in the parser but if I 
>>> move it down the stack a bit this is probably doable.
>>
>> Please don't. Having `=> expr` be simple syntax sugar for `{ return 
>> expr; }` is consistent and easy to understand.

Yes, no need to change the implementation of this feature, just fix 
semantic analysis of constructors.

>> We don't need to add 
>> special cases just to save a *single character*:
>> ...

Sure, but actually, the fact that the example code does not already work 
with the current implementation of the feature is the special case. 
There is even less need to add special cases just so people have to 
waste an additional character. (Plus some white space, by the way, at 
least outside of personal projects. There may be strict style guidelines.)

>>     this(string y) => this(0, y);
>>     this(string y) { this(0, y); }
> ...

If you have to violate common style guidelines in order to support a 
claim that the status quo is not so much worse, then probably the new 
syntax is actually significantly better. (Razvan did the same in the 
feedback thread, I don't get why people are doing this. Would this 
really fly, e.g., in Phobos?)

> Actually, the following compiles:
> ```d
> void funcc()
> {
> }
> 
> void func()
> {
>      return funcc();
> }
> void main()
> {
>      func();
> 
> }
> ```
> So maybe the fact that `this(string y) => this(0, y);` doesn't compile 
> is a compiler bug? Constructors return `void` after all, no?

I think so, or at least it's an undesirable special case:

```d
void foo(){ return; }
struct S{
     this(int x){ return; } // ok, can return void
     this(int x,int y){ return foo(); } // error
}
```

"Error: cannot return expression from constructor"