com.jnape.palatable.lambda.adt.coproduct

Interface CoProduct2<A,B,CP2 extends CoProduct2<A,B,?>>

Type Parameters:

A - the first possible type

B - the second possible type

CP2 - the recursive type of this coproduct (used for embedding)

All Known Implementing Classes:

Choice2, Either, Maybe, RecursiveResult, Try

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface CoProduct2<A,B,CP2 extends CoProduct2<A,B,?>>

A generalization of the coproduct of two types. Coproducts represent the disjoint union of two or more distinct types, and provides an interface for specifying morphisms from those types to a common result type.

Learn more about Coproducts.

See Also:

Choice2, Either

Method Summary

Modifier and Type	Method and Description
default <C> CoProduct3<A,B,C,? extends CoProduct3<A,B,C,?>>	diverge() Diverge this coproduct by introducing another possible type that it could represent.
default <R> R	embed(Fn1<? super CP2,? extends R> aFn, Fn1<? super CP2,? extends R> bFn) Embed this coproduct inside another value; that is, given morphisms from this coproduct to R, apply the appropriate morphism to this coproduct as a whole.
default CoProduct2<B,A,? extends CoProduct2<B,A,?>>	invert() Swap the type parameters.
<R> R	match(Fn1<? super A,? extends R> aFn, Fn1<? super B,? extends R> bFn) Type-safe convergence requiring a match against all potential types.
default Product2<Maybe<A>,Maybe<B>>	project() Project this coproduct onto a product, such that the index in the product that corresponds to this coproduct's value is present, while the other indices are absent.
default Maybe<A>	projectA() Convenience method for projecting this coproduct onto a product and then extracting the first slot value.
default Maybe<B>	projectB() Convenience method for projecting this coproduct onto a product and then extracting the second slot value.

Method Detail

match

<R> R match(Fn1<? super A,? extends R> aFn,
            Fn1<? super B,? extends R> bFn)

Type-safe convergence requiring a match against all potential types.

Type Parameters:

R - result type

Parameters:

aFn - morphism A -> R

bFn - morphism B -> R

Returns:

the result of applying the appropriate morphism to this coproduct's unwrapped value

diverge

default <C> CoProduct3<A,B,C,? extends CoProduct3<A,B,C,?>> diverge()

Diverge this coproduct by introducing another possible type that it could represent. As no morphisms can be provided mapping current types to the new type, this operation merely acts as a convenience method to allow the use of a more convergent coproduct with a more divergent one; that is, if a CoProduct3<String, Integer, Boolean> is expected, a CoProduct2<String, Integer> should suffice.

Generally, we use inheritance to make this a non-issue; however, with coproducts of differing magnitudes, we cannot guarantee variance compatibility in one direction conveniently at construction time, and in the other direction, at all. A CoProduct2 could not be a CoProduct3 without specifying all type parameters that are possible for a CoProduct3 - more specifically, the third possible type - which is not necessarily known at construction time, or even useful if never used in the context of a CoProduct3. The inverse inheritance relationship - CoProduct3 < CoProduct2 - is inherently unsound, as a CoProduct3 cannot correctly implement match(com.jnape.palatable.lambda.functions.Fn1<? super A, ? extends R>, com.jnape.palatable.lambda.functions.Fn1<? super B, ? extends R>), given that the third type C is always possible.

For this reason, there is a diverge method supported between all CoProduct types of single magnitude difference.

Type Parameters:

C - the additional possible type of this coproduct

Returns:

a CoProduct3<A, B, C>

project

default Product2<Maybe<A>,Maybe<B>> project()

Project this coproduct onto a product, such that the index in the product that corresponds to this coproduct's value is present, while the other indices are absent.

Returns:

a product of the coproduct projection

projectA

default Maybe<A> projectA()

Convenience method for projecting this coproduct onto a product and then extracting the first slot value.

Returns:

an optional value representing the projection of the "a" type index

projectB

default Maybe<B> projectB()

Convenience method for projecting this coproduct onto a product and then extracting the second slot value.

Returns:

an optional value representing the projection of the "b" type index

invert

default CoProduct2<B,A,? extends CoProduct2<B,A,?>> invert()

Swap the type parameters.

Returns:

The inverted coproduct

embed

default <R> R embed(Fn1<? super CP2,? extends R> aFn,
                    Fn1<? super CP2,? extends R> bFn)

Embed this coproduct inside another value; that is, given morphisms from this coproduct to R, apply the appropriate morphism to this coproduct as a whole. Like match(com.jnape.palatable.lambda.functions.Fn1<? super A, ? extends R>, com.jnape.palatable.lambda.functions.Fn1<? super B, ? extends R>), but without unwrapping the value.

Type Parameters:

R - result type

Parameters:

aFn - morphism A v B -> R, applied in the A case

bFn - morphism A v B -> R, applied in the B case

Returns:

the result of applying the appropriate morphism to this coproduct