Lens#toIso for converting a lens to an iso

jnape · jnape · commit 6c91e649e4e5 · 2018-05-26T16:55:22.000-05:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -4,6 +4,9 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/).
 
 ## [Unreleased]
+### Added
+- `Lens#toIso`, for converting a lens to an iso
+
 ### Fixed
 - Deforested iterables execute in intended nesting order, where essential
 
diff --git a/src/main/java/com/jnape/palatable/lambda/lens/Lens.java b/src/main/java/com/jnape/palatable/lambda/lens/Lens.java
@@ -10,6 +10,7 @@
 import java.util.function.BiFunction;
 import java.util.function.Function;
 
+import static com.jnape.palatable.lambda.lens.Iso.iso;
 import static com.jnape.palatable.lambda.lens.Lens.Simple.adapt;
 import static com.jnape.palatable.lambda.lens.functions.Over.over;
 import static com.jnape.palatable.lambda.lens.functions.Set.set;
@@ -209,6 +210,16 @@ default <Z> Lens<S, T, A, Z> mapB(Function<? super Z, ? extends B> fn) {
         return lens(view(this), (s, z) -> set(this, fn.apply(z), s));
     }
 
+    /**
+     * Produce an {@link Iso} from this {@link Lens} by providing a default <code>S</code> value.
+     *
+     * @param s the default <code>S</code>
+     * @return an {@link Iso}
+     */
+    default Iso<S, T, A, B> toIso(S s) {
+        return iso(view(this), set(this).flip().apply(s));
+    }
+
     /**
      * Left-to-right composition of lenses. Requires compatibility between S and T.
      *
diff --git a/src/test/java/com/jnape/palatable/lambda/lens/LensTest.java b/src/test/java/com/jnape/palatable/lambda/lens/LensTest.java
@@ -103,4 +103,11 @@ public void bothForSimpleLenses() {
         assertEquals(tuple(3, '3'), view(both(stringToInt, stringToChar), "3"));
         assertEquals("133", set(both(stringToInt, stringToChar), tuple(3, '3'), "1"));
     }
+
+    @Test
+    public void toIso() {
+        Iso<List<String>, Set<Integer>, String, Integer> iso = LENS.toIso(singletonList(""));
+        assertEquals("1", view(iso, asList("1", "2", "3")));
+        assertEquals(singleton(1), view(iso.mirror(), 1));
+    }
 }

Original file line number	Diff line number	Diff line change
`@@ -103,4 +103,11 @@ public void bothForSimpleLenses() {`
`103`	`103`	`assertEquals(tuple(3, '3'), view(both(stringToInt, stringToChar), "3"));`
`104`	`104`	`assertEquals("133", set(both(stringToInt, stringToChar), tuple(3, '3'), "1"));`
`105`	`105`	`}`
	`106`	`+`
	`107`	`+ @Test`
	`108`	`+ public void toIso() {`
	`109`	`+ Iso<List<String>, Set<Integer>, String, Integer> iso = LENS.toIso(singletonList(""));`
	`110`	`+ assertEquals("1", view(iso, asList("1", "2", "3")));`
	`111`	`+ assertEquals(singleton(1), view(iso.mirror(), 1));`
	`112`	`+ }`
`106`	`113`	`}`