Context:
    data + GUI List

Goal:
    auto list = new List( data );

Concept:
    class is created in the usual way : new List( data )
    store inside the class            : T data;
    type T deducted                   : ( T )( T data )


Tried way:
    template List( T )
    {
        class List
        {
            T data;

            this( T data )
            {
                this.data = data;
            }


            // data usage...
        }
    }


    void main()
    {
        string[] extensions = [ ".d", ".di" ];

    	auto list = new List( extensions );
    }


    Source: https://run.dlang.io/is/Bw2zHB

Question:
    How to implement on D beauty clean flexible code ?
    like a:
        auto list = new List( data );

    How to return from 'List( data )' class type ?

On Saturday, 23 January 2021 at 05:39:18 UTC, Виталий Фадеев wrote:
> Context:
>     data + GUI List
>
> Goal:
>     auto list = new List( data );

Of course, we can use 'factory':

    import std.stdio;


    template List( alias T )
    {
        class List
        {
            T data;

            this( T data )
            {
                this.data = data;
            }


            // data usage...
        }
    }


    auto  listFactory( T )( T data )
    {
        return new List!( T )( data );
    }

    void main()
    {
        string[] extensions = [ ".d", ".di" ];

        auto list = listFactory( extensions );

        //auto list = new List( extensions );
    }

    source: https://run.dlang.io/is/y167tu


But, how to create class instance with type deduction in usual way ?

    auto list = new List( extensions );

On Saturday, 23 January 2021 at 05:54:09 UTC, Виталий Фадеев wrote:
> But, how to create class instance with type deduction in usual way ?
>
>     auto list = new List( extensions );

You can't; there's no type deduction for constructors.

On Saturday, 23 January 2021 at 05:54:09 UTC, Виталий Фадеев wrote:
>     auto  listFactory( T )( T data )
>     {
>         return new List!( T )( data );
>     }

This is the correct way to do it in D; it's annoying, I know. (Personally, I usually shorten `listFactory` to just `list` to make the name as similar as possible to the type name, without actually causing a collision.)

On Saturday, 23 January 2021 at 05:54:09 UTC, Виталий Фадеев wrote:
> On Saturday, 23 January 2021 at 05:39:18 UTC, Виталий Фадеев wrote:
>> Context:
>>     data + GUI List
>>
>> Goal:
>>     auto list = new List( data );

I want 'this( T )( T data )' deduction:

    class A( T )
    {
        this( T )( T data )
        {
            // ...
        }
    }

What way to implement this ?

Rules:
   1. if class is template
   2. if ctor is template
   3. if ctor template arg have same name with class template arg name (example: T )
   4. deduct T of ctor
   5. set type T for class template ( or put in suggestion queue )

Verify, please.

Where source ?
Where deduction implementation ?

On Saturday, 23 January 2021 at 07:17:38 UTC, Виталий Фадеев wrote:
> Where source ?
> Where deduction implementation ?

Here:

https://github.com/dlang/dmd/blob/v2.095.0/src/dmd/dtemplate.d#L1308

On Saturday, 23 January 2021 at 19:19:29 UTC, Paul Backus wrote:
> On Saturday, 23 January 2021 at 07:17:38 UTC, Виталий Фадеев wrote:
>> Where source ?
>> Where deduction implementation ?
>
> Here:
>
> https://github.com/dlang/dmd/blob/v2.095.0/src/dmd/dtemplate.d#L1308

Thank!