Re: Chained call pattern with inheritance, polymorphism and generics...

On Sep 28, 6:57 pm, Roedy Green <see_webs...@mindprod.com.invalid>
wrote:


What if I changed it to this:

public class BaseBuilder<T> {
    private String something;
    public T something(String something) {
       this.something = something;
       return getChainTarget();
    }

    protected abstract T getChainLink();
}

public class SpecificBuilder extends BaseBuilder<SpecificBuilder> {

    private String other;

    public SpecificBuilder other(String other) {
        this.other = other;
    }

    protected SpecificBuilder getChainLink() {
     return this;
   }
}

SpecificBuilder b = new
SpecificBuilder().something("Hello").other("World!");

This works since something() returns T, which in SpecificBuilder IS
SpecificBuilder.

The problem with my solution is that I can't have:

class MoreSpecificBuilder extends SpecificBuilder {
    public void doMore() {
    }
    protected MoreSpecificBuilder getChainLink() {
     return this;
   }
}

new MoreSpecificBuilder().something("hello").doMore(); // whoops!

If "something()'s" return type could be "the compile time type of the
reference to this object", a.k.a ThisType, then it would work just
fine. Unfortunately, thats not yet a feature. Makes one long for a
weakly typed language :-)