Is there any way to simulate the cascade operator (..) of Dart in D? This operator makes fluid initialization simple.

I am using Dart for code generation but would like to consider D if I can find a convenient replacement for the following declarative style:

    var dateRange = struct('date_range')
      ..doc = 'Basic pair of start and end dates'
      ..unitTest = true
      ..publicSection = true
      ..members = [
        member('start_date')
        ..type = 'Date',
        member('end_date')
        ..type = 'Date',
      ];

So struct is a function that returns an instance of Struct.

    class Struct extends Decls {
      ...
      /// Documentation for this D struct
      String doc;
      /// List of members of this class
      List<Member> members = [];
      bool unitTest = false;
      ...
    }

..doc = ... assigns to the Struct.doc field and returns the original Struct instance so that ..unitTest = true can be applied to the original Struct instance, etc.

What is the best way to achieve simple declarative style for very large initialization objects?

Thanks,
Dan

Daniel Davidson:

> I am using Dart for code generation but would like to consider D if I can find a convenient replacement for the following declarative style:

Replacing Dart with D seems quite strange, such two languages have so much different usage niches.


>     var dateRange = struct('date_range')
>       ..doc = 'Basic pair of start and end dates'
>       ..unitTest = true
>       ..publicSection = true
>       ..members = [
>         member('start_date')
>         ..type = 'Date',
>         member('end_date')
>         ..type = 'Date',
>       ];

A similar syntax is not allowed in D, but there are two things that help for this: the C-style initialization of structs, that support field names too, and the with(){} statement.

Bye,
bearophile

On Thursday, 12 September 2013 at 19:41:49 UTC, bearophile wrote:
> Daniel Davidson:
>
>> I am using Dart for code generation but would like to consider D if I can find a convenient replacement for the following declarative style:
>
> Replacing Dart with D seems quite strange, such two languages have so much different usage niches.
>
>
>>    var dateRange = struct('date_range')
>>      ..doc = 'Basic pair of start and end dates'
>>      ..unitTest = true
>>      ..publicSection = true
>>      ..members = [
>>        member('start_date')
>>        ..type = 'Date',
>>        member('end_date')
>>        ..type = 'Date',
>>      ];
>
> A similar syntax is not allowed in D, but there are two things that help for this: the C-style initialization of structs, that support field names too, and the with(){} statement.
>
> Bye,
> bearophile

The problem with with is the name can not hide each other, so it is easy to get into trouble. With C-style initialization I don't think you can use as expression - I think you need an lvalue for each and this hurts nesting.

I have a style I'm playing with and if anyone has comments or improvements (i.e. make more succinct/readable) it would be appreciated.

Here is a sample and the source for this and comparable Dart are in the links.

    auto d = make((ref Dossier _) {
      _.family = [
       "father" : make((ref Person _) {
           _.birthDate = "2001/1/1";
           _.deathDate = "2101/1/1";
           _.retirementDate = "2100/1/1"; }),
       "mother" : make((ref Person _) {
           _.birthDate = "2005/1/1";
           _.deathDate = "2125/1/1";
           _.retirementDate = "2100/1/1"; }),
       ];
      _.assets = [
       "house" : make((ref Asset _) {
           _.name = "Home on the Hill";
           _.unitValue = 120_000; }),
       "car" : make((ref Asset _) {
           _.name = "Dodge Dart";
           _.unitValue = 500; })
      ];
    });

http://pastebin.com/iLVL20Bz
http://pastebin.com/mLcWDACm

Thanks
Dan