com.jnape.palatable.lambda.semigroup.builtin.MaxBy Maven / Gradle / Ivy

Go to download
package com.jnape.palatable.lambda.semigroup.builtin;

import com.jnape.palatable.lambda.functions.Fn1;
import com.jnape.palatable.lambda.functions.specialized.SemigroupFactory;
import com.jnape.palatable.lambda.semigroup.Semigroup;

import java.util.function.Function;

import static com.jnape.palatable.lambda.functions.builtin.fn3.LTBy.ltBy;

/**
 * Given a mapping function from some type A to some {@link Comparable} type B, produce a
 * {@link Semigroup} over A that chooses between two values x and y via the
 * following rules:
 * 
 * If x is strictly less than y in terms of B, return y
 * Otherwise, return x
 * 
 *
 * @param  the value type
 * @param  the mapped comparison type
 * @see Max
 * @see MinBy
 */
public final class MaxBy> implements SemigroupFactory, A> {

    private static final MaxBy INSTANCE = new MaxBy();

    private MaxBy() {
    }

    @Override
    public Semigroup apply(Function compareFn) {
        return (x, y) -> ltBy(compareFn, y, x) ? y : x;
    }

    @SuppressWarnings("unchecked")
    public static > MaxBy maxBy() {
        return INSTANCE;
    }

    public static > Semigroup maxBy(
            Function compareFn) {
        return MaxBy.maxBy().apply(compareFn);
    }

    public static > Fn1 maxBy(Function compareFn, A x) {
        return MaxBy.maxBy(compareFn).apply(x);
    }

    public static > A maxBy(Function compareFn, A x, A y) {
        return maxBy(compareFn, x).apply(y);
    }
}