Bug 9825 – Add ability to auto-generate a specific field constructor

Let's say you have a Rectangle struct: struct Rect { int x; int y; int width; int height; } Later on you add two additional structures: struct Point { int x; int y; } struct Size { int width; int height; } So as a convenience you want to enable constructing a Rect with these types: struct Rect { int x; int y; int width; int height; /** Construct from Point and Size. */ this(Point point, Size size) { this.x = point.x; this.y = point.y; this.width = size.width; this.height = size.height; } } However this disables the default field-based constructor. We should have the ability to explicitly reintroduce the field-based constructor. But to avoid accidentally generating the field constructor for *any* field we can take advantage of the 'default' keyword for marking which fields should be part of a default ctor. For example: struct S { // non-default ctor this(string first, string last) { this.name = first ~ last; } string fullname; default: int field1; int field2; } Here a default constructor would be generated that only initializes the fields marked as 'default', in other words the above can be constructed with: auto s1 = S("John", "Doe"); // custom ctor auto s2 = S(1, 2); // default ctor The benefit here is that a default ctor is only generated for fields marked as default, meaning that introducing new non-default fields does not update the default ctor. Perhaps the feature could be incorporated for classes too.

I hate this idea now, too much complications, and an added additional meaning for the default keyword. Anywho a mixin can just as easily be used.