com.jnape.palatable.lambda.optics.lenses

Class ListLens

java.lang.Object

com.jnape.palatable.lambda.optics.lenses.ListLens

public final class ListLens
extends Object

Lenses that operate on Lists.

Method Summary

Modifier and Type	Method and Description
static <X> Lens.Simple<List<X>,List<X>>	asCopy() Convenience static factory method for creating a lens over a copy of a list.
static <X> Lens.Simple<List<X>,Maybe<X>>	elementAt(int index) Convenience static factory method for creating a lens that focuses on an element in a list at a particular index.
static <X> Lens.Simple<List<X>,X>	elementAt(int index, X defaultValue) Convenience static factory method for creating a lens that focuses on an element in a list at a particular index, returning defaultValue if there is no value at that index.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

asCopy

public static <X> Lens.Simple<List<X>,List<X>> asCopy()

Convenience static factory method for creating a lens over a copy of a list. Useful for composition to avoid mutating a list reference.

Type Parameters:

X - the list element type

Returns:

a lens that focuses on copies of lists

elementAt

public static <X> Lens.Simple<List<X>,Maybe<X>> elementAt(int index)

Convenience static factory method for creating a lens that focuses on an element in a list at a particular index. Wraps result in a Maybe to handle null values or indexes that fall outside of list boundaries.

Type Parameters:

X - the list element type

Parameters:

index - the index to focus on

Returns:

Maybe the element at the index

elementAt

public static <X> Lens.Simple<List<X>,X> elementAt(int index,
                                                   X defaultValue)

Convenience static factory method for creating a lens that focuses on an element in a list at a particular index, returning defaultValue if there is no value at that index.

Note that this lens is NOT lawful, since "putting back what you got changes nothing" fails for any value B where S is the empty list

Type Parameters:

X - the list element type

Parameters:

index - the index to focus on

defaultValue - the value to use if there is no element at index

Returns:

the element at the index, or defaultValue