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digitalmars.D.announce - Would this be a useful construct to add to D? auto for constructor

reply Chris Katko <ckatko gmail.com> writes:
```D
class dataGridLayerView{
    int t;
    this(int _t){
       t = _t;
       }
    }

class myClass{
    dataGridLayerView dataGrid;

    this()
       {
       dataGrid = new auto(15); // <--- new
       // instead of
       dataGrid = new dataGridLayerView(15);
       }
    }
```

Because it seems, conceptually, the compiler should know all the 
details required here to simply insert the right constructor 
name. Basically just the reverse of:

```D
auto t = sqrt(15);
```

So intuitively it makes sense to me.

It might even be possible to write a mixin to do this, I'm not 
sure.

I'm no D wizard, but I don't see any obvious name or lexing 
conflicts/ambiguity.

Cheers,
--Chris
Jan 22
parent reply Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Monday, January 22, 2024 11:05:28 PM MST Chris Katko via Digitalmars-d-
announce wrote:

 ```D
 class dataGridLayerView{
     int t;
     this(int _t){
        t = _t;
        }
     }

 class myClass{
     dataGridLayerView dataGrid;

     this()
        {
        dataGrid = new auto(15); // <--- new
        // instead of
        dataGrid = new dataGridLayerView(15);
        }
     }
 ```

 Because it seems, conceptually, the compiler should know all the
 details required here to simply insert the right constructor
 name. Basically just the reverse of:

 ```D
 auto t = sqrt(15);
 ```

 So intuitively it makes sense to me.

 It might even be possible to write a mixin to do this, I'm not
 sure.

 I'm no D wizard, but I don't see any obvious name or lexing
 conflicts/ambiguity.

 Cheers,
 --Chris


This is the wrong forum for questions. This is for announcements.

https://forum.dlang.org/group/general is for general discussions on D.

https://forum.dlang.org/group/learn is for asking questions about using D.

In any case, as far as your question goes, it is unlikely that a feature
like that would be implemented, because expressions in D do not typically
get their type from what they're assigned to. The type of the expression is
determined separately from where it is used, and then it's checked to see
whether it works where it's being used. There are a few exceptions (mostly
having to do with initializing variables from array literals), so I don't
know that the chances of adding a feature like this are zero, but I don't
think that they're high.

That being said, I expect that it would be pretty easy to write a mixin to
do something like that if you really wanted to. Also, if you're simply
looking to not have to name the type, you could do

dataGrid = new typeof(datagrid)(15);

- Jonathan M Davis
Jan 22
parent reply ryuukk_ <ryuukk.dev gmail.com> writes:
On Tuesday, 23 January 2024 at 06:30:08 UTC, Jonathan M Davis 
wrote:

 That being said, I expect that it would be pretty easy to write 
 a mixin to do something like that if you really wanted to. 
 Also, if you're simply looking to not have to name the type, 
 you could do

 dataGrid = new typeof(datagrid)(15);

 - Jonathan M Davis


You like to turn off people before they get the chance to develop 
further, this is bad

You should try more languages, it'll be eye opener

``dataGrid = new typeof(datagrid)(15);`` is both, verbose and ugly

Besides, you seem to have missed this:

https://github.com/dlang/DIPs/blob/e2ca557ab9d3e60305a37da0d5b58299e0a9de0e/DIPs/DIP1044.md

https://github.com/dlang/dmd/pull/14650

It could be expanded with structs/classes

So your "it can't be done" argument is already wrong
Jan 23
next sibling parent Sergey <kornburn yandex.ru> writes:
On Tuesday, 23 January 2024 at 11:11:00 UTC, ryuukk_ wrote:
[OT] btw what did you find? Which one could you recommend? 
https://forum.dlang.org/post/cqgrciflmvuwonsnzjec forum.dlang.org
Jan 23
prev sibling next sibling parent Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Tuesday, January 23, 2024 4:11:00 AM MST ryuukk_ via Digitalmars-d-announce 
wrote:

 On Tuesday, 23 January 2024 at 06:30:08 UTC, Jonathan M Davis

 wrote:

 That being said, I expect that it would be pretty easy to write
 a mixin to do something like that if you really wanted to.
 Also, if you're simply looking to not have to name the type,
 you could do

 dataGrid = new typeof(datagrid)(15);

 - Jonathan M Davis


 You like to turn off people before they get the chance to develop
 further, this is bad

 You should try more languages, it'll be eye opener

 ``dataGrid = new typeof(datagrid)(15);`` is both, verbose and ugly

 Besides, you seem to have missed this:

 https://github.com/dlang/DIPs/blob/e2ca557ab9d3e60305a37da0d5b58299e0a9de0e/
 DIPs/DIP1044.md

 https://github.com/dlang/dmd/pull/14650

 It could be expanded with structs/classes

 So your "it can't be done" argument is already wrong


I never said that it couldn't be done. I said that it goes against how
expressions and assignment in D normally work, so it's probably not a change
that would be accepted. And the DIP and PR that you linked to have been
rejected. If the OP wants to push for a change like this, then they can, and
they might get lucky, but I would expect it to be rejected.

Either way, there are ways to do something similar with what we already
have, so I pointed them out. While you might not like a solution like using
typeof, it is an option that someone can use right now regardless of what
improvements we get in the future.

- Jonathan M Davis
Jan 23
prev sibling parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On Tuesday, 23 January 2024 at 11:11:00 UTC, ryuukk_ wrote:

 On Tuesday, 23 January 2024 at 06:30:08 UTC, Jonathan M Davis 
 wrote:

 That being said, I expect that it would be pretty easy to 
 write a mixin to do something like that if you really wanted 
 to. Also, if you're simply looking to not have to name the 
 type, you could do

 dataGrid = new typeof(datagrid)(15);


 You like to turn off people before they get the chance to 
 develop further, this is bad


Would you like to encourage proposals/work/effort that will 
ultimately not be accepted? I don't. I would rather tell someone 
no early than tell them no later. And I agree with Jonathan, zero 
proposals that infer type from how they are used have been 
accepted by Walter, this one probably will be no different.

To the OP, I think the value of the feature needs to be more than 
just avoiding repeating the name of the type.

You also can do some library tricks (unfortunately this won't 
count as construction, but probably is fine in most cases)

```d
auto create(T, Args...)(out T val, Args args)
{
    static if(is(T == class))
       val = new T(args);
    else static if(...) // do eveyrything else.
}

...

dataGrid.create(15);
```

-Steve
Jan 23
parent reply Walter Bright <newshound2 digitalmars.com> writes:
On 1/23/2024 8:01 AM, Steven Schveighoffer wrote:

 zero proposals that infer type from how they are used 
 have been accepted by Walter, this one probably will be no different.


Types are inferred in D from the bottom up. Mixing in special cases of it being 
top down leads to confusion over how the type is determined.
Jan 24
parent Chris Katko <ckatko gmail.com> writes:
On Wednesday, 24 January 2024 at 08:22:49 UTC, Walter Bright 
wrote:

 On 1/23/2024 8:01 AM, Steven Schveighoffer wrote:

 zero proposals that infer type from how they are used have 
 been accepted by Walter, this one probably will be no 
 different.


 Types are inferred in D from the bottom up. Mixing in special 
 cases of it being top down leads to confusion over how the type 
 is determined.


Thanks to everyone for the feedback. And sorry I selected the 
wrong forum. Apologies,
--Chris
Jan 27