/**
  * Copyright (c): Uwe Schmidt, FH Wedel
  *
  * You may study, modify and distribute this source code
  * FOR NON-COMMERCIAL PURPOSES ONLY.
  * This copyright message has to remain unchanged.
  *
  * Note that this document is provided 'as is',
  * WITHOUT WARRANTY of any kind either expressed or implied.
  */

package ds.util;

abstract public
    class Function<X,Y> {

    abstract public Y apply(X x);

    // create identity functions

    public static <X> Function<X,X> id() {
	return
	    new Function<X,X>() {
	    public X apply(X x) {
		return
		    x;
	    }
	};
    }

    // create const functions

    public static <X,Y> Function<X,Y> constF(Y c) {
	return
	    new Const<X,Y>(c);
    }

    private static
	class Const<X,Y> extends Function<X,Y> {
	private final Y c;

	public Const(Y c) { this.c = c; }

	public Y apply(X x) {
	    return
		c;
	}
    }
}