Named constructors

[Olivier FAURE]

On Monday, 14 January 2019 at 16:04:26 UTC, Atila Neves wrote:
> On Monday, 14 January 2019 at 14:31:09 UTC, aliak wrote:
>> auto a = Builder()
>>   .accountNumber(202)
>>   .firstName("Bob")
>>   .lastName("Who")
>>   .branch("N-2")
>>   .interest(20.0)
>>   .balance(10.0)
>>   .build()
>>
>> ??
>
> auto a = Customer(AccountNumber(202),
>                   FirstName("Bob"),
>                   LastName("Who"),
>                   Branch("N-2"),
>                   Interest(20.0),
>                   Balance(10.0));
>
> struct Customer {
>     this(A...)(auto ref A args) 
> if(constraintVerifyingNumberAndTypesOfArgs!A) {
>         this.accountNumber = args[staticIndexOf!(AccountNumber, 
> A)];
>         // etc.
>     }
> }

I think these design patterns are useful if you really want named 
arguments in your code right now, but they really shouldn't 
replace the structure initialization DIP.

Personally speaking, I hate having hacks like these in my code 
and would immensely prefer an idiomatic syntax eg:

     auto a = Customer{ accountNumber: 202, fistName: "Bob" };

which would produce easy-to-read error messages like:

     Error: `fistName` is not a member of `Customer`. Did you mean 
`firstName`?

     Error: Initialization list for `Customer` does not provide 
value for member variable `lastName`, which has no default value 
defined.

I'm having trouble guessing what error messages your Customer 
structure would provide, but I imagine they wouldn't be nearly as 
informative. Same thing for generated documentation.