Auto constructor [Was: Archetype language]

[Don]

spir wrote:
> On 03/21/2011 12:55 AM, bearophile wrote:
>> Among the things I've listed about Archetype there's one interesting 
>> thing. Class instances aren't PODs, but sometimes I prefer reference 
>> semantics and to populate fields in a plain way, expecially for simple 
>> classes.
>>
>> Time ago I and other people have suggested a syntax like (this also to 
>> avoid a class of bugs 
>> http://d.puremagic.com/issues/show_bug.cgi?id=3878 ):
>>
>>
>> class Foo {
>>    string x;
>>    int y = 1;
>>    this(this.x, this.y) {}
>> }
>> void main() {
>>    Foo f3 = new Foo("hello", 10);
>> }
>>
>>
>> A simpler solution are classes with automatic constructors:
>>
>> class Foo {
>>    string x;
>>    int y = 1;
>> }
>> void main() {
>>    Foo f1 = new Foo(); // Good
>>    Foo f2 = new Foo("hello"); // Good
>>    Foo f3 = new Foo("hello", 10); // Good
>> }
>>
>>
>> What kind of problems are caused by this? :-)
>>
>>
>> Currently that syntax is supported for structs created as values, but 
>> not for structs created by pointer:
>>
>> struct Foo {
>>    string x;
>>    int y = 1;
>> }
>> void main() {
>>    Foo* f1 = new Foo(); // OK
>>    Foo* f2 = new Foo("hello"); // Error: no constructor for Foo
>>    Foo* f3 = new Foo("hello", 10); // Error: no constructor for Foo
>> }
> 
> I definitely want some feature like that in D.
> 
> Have no idea why a default seems complicated for classes while structs 
> have it.

It's not that it's complicated, it's that for structs, the ordering of 
their members is part of the public interface. For classes, the members 
are not public.