com.jnape.palatable.lambda.optics.lenses

Class MapLens

java.lang.Object

com.jnape.palatable.lambda.optics.lenses.MapLens

public final class MapLens
extends Object

Lenses that operate on Maps.

Method Summary

Modifier and Type	Method and Description
static <K,V> Lens.Simple<Map<K,V>,Map<K,V>>	asCopy() A lens that focuses on a copy of a Map.
static <M extends Map<K,V>,K,V> Lens<Map<K,V>,M,M,M>	asCopy(Fn1<? super Map<K,V>,? extends M> copyFn) A lens that focuses on a copy of a Map as a subtype M.
static <K,V> Lens.Simple<Map<K,V>,Map<V,K>>	inverted() A lens that focuses on the inverse of a map (keys and values swapped).
static <K,V> Lens.Simple<Map<K,V>,Set<K>>	keys() A lens that focuses on the keys of a map.
static <K,V,V2> Lens.Simple<Map<K,V>,Map<K,V2>>	mappingValues(Iso<V,V,V2,V2> iso) A lens that focuses on a map while mapping its values with the mapping Iso.
static <M extends Map<K,V>,K,V> Lens<Map<K,V>,M,Maybe<V>,Maybe<V>>	valueAt(Fn1<? super Map<K,V>,? extends M> copyFn, K k) A lens that focuses on a value at a key in a map, as a Maybe, and produces a subtype M on the way back out.
static <K,V> Lens.Simple<Map<K,V>,Maybe<V>>	valueAt(K k) A lens that focuses on a value at a key in a map, as a Maybe.
static <K,V> Lens.Simple<Map<K,V>,V>	valueAt(K k, V defaultValue) A lens that focuses on a value at a key in a map, falling back to defaultV if the value is missing.
static <K,V> Lens.Simple<Map<K,V>,Collection<V>>	values() A lens that focuses on the values of a map.

Methods inherited from class java.lang.Object

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

Method Detail

asCopy

public static <M extends Map<K,V>,K,V> Lens<Map<K,V>,M,M,M> asCopy(Fn1<? super Map<K,V>,? extends M> copyFn)

A lens that focuses on a copy of a Map as a subtype M. Useful for composition to avoid mutating a map reference.

Type Parameters:

M - the map subtype

K - the key type

V - the value type

Parameters:

copyFn - the copy function

Returns:

a lens that focuses on copies of maps as a specific subtype

asCopy

public static <K,V> Lens.Simple<Map<K,V>,Map<K,V>> asCopy()

A lens that focuses on a copy of a Map. Useful for composition to avoid mutating a map reference.

Type Parameters:

K - the key type

V - the value type

Returns:

a lens that focuses on copies of maps

valueAt

public static <M extends Map<K,V>,K,V> Lens<Map<K,V>,M,Maybe<V>,Maybe<V>> valueAt(Fn1<? super Map<K,V>,? extends M> copyFn,
                                                                                  K k)

A lens that focuses on a value at a key in a map, as a Maybe, and produces a subtype M on the way back out.

Type Parameters:

M - the map subtype

K - the key type

V - the value type

Parameters:

copyFn - the copy function

k - the key to focus on

Returns:

a lens that focuses on the value at key, as a Maybe

valueAt

public static <K,V> Lens.Simple<Map<K,V>,Maybe<V>> valueAt(K k)

A lens that focuses on a value at a key in a map, as a Maybe.

Type Parameters:

K - the key type

V - the value type

Parameters:

k - the key to focus on

Returns:

a lens that focuses on the value at key, as a Maybe

valueAt

public static <K,V> Lens.Simple<Map<K,V>,V> valueAt(K k,
                                                    V defaultValue)

A lens that focuses on a value at a key in a map, falling back to defaultV if the value is missing.

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 map

Type Parameters:

K - the key type

V - the value type

Parameters:

k - the key to focus on

defaultValue - the default value to use in case of a missing value at key

Returns:

a lens that focuses on the value at the key

keys

public static <K,V> Lens.Simple<Map<K,V>,Set<K>> keys()

A lens that focuses on the keys of a map.

Type Parameters:

K - the key type

V - the value type

Returns:

a lens that focuses on the keys of a map

values

public static <K,V> Lens.Simple<Map<K,V>,Collection<V>> values()

A lens that focuses on the values of a map. In the case of updating the map, only the entries with a value listed in the update collection of values are kept.

Note that this lens is NOT lawful, since "you get back what you put in" fails for all values B that represent a non-surjective superset of the existing values in S.

Type Parameters:

K - the key type

V - the value type

Returns:

a lens that focuses on the values of a map

inverted

public static <K,V> Lens.Simple<Map<K,V>,Map<V,K>> inverted()

A lens that focuses on the inverse of a map (keys and values swapped). In the case of multiple equal values becoming keys, the last one wins.

Note that this lens is very likely to NOT be lawful, since "you get back what you put in" will fail for any keys that map to the same value.

Type Parameters:

K - the key type

V - the value type

Returns:

a lens that focuses on the inverse of a map

mappingValues

public static <K,V,V2> Lens.Simple<Map<K,V>,Map<K,V2>> mappingValues(Iso<V,V,V2,V2> iso)

A lens that focuses on a map while mapping its values with the mapping Iso.

Note that for this lens to be lawful, iso must be lawful.

Type Parameters:

K - the key type

V - the unfocused map value type

V2 - the focused map value type

Parameters:

iso - the mapping Iso

Returns:

a lens that focuses on a map while mapping its values