com.jnape.palatable.lambda.functor.builtin.Identity Maven / Gradle / Ivy

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package com.jnape.palatable.lambda.functor.builtin;

import com.jnape.palatable.lambda.functor.Functor;

import java.util.function.Function;

/**
 * A functor over some value of type A that can be mapped over and retrieved later.
 *
 * @param  the value type
 */
public final class Identity implements Functor {

    private final A a;

    public Identity(A a) {
        this.a = a;
    }

    /**
     * Retrieve the value.
     *
     * @return the value
     */
    public A runIdentity() {
        return a;
    }

    /**
     * Covariantly map over the value.
     *
     * @param fn  the mapping function
     * @param  the new value type
     * @return an Identity over B (the new value)
     */
    @Override
    public  Identity fmap(Function fn) {
        return new Identity<>(fn.apply(a));
    }
}