Chaining nullable lenses part 2

dmcg · Dec 30, 2023 · 9de9031 · 9de9031
1 parent 66bd0b4
commit 9de9031
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Showing 2 changed files with 29 additions and 8 deletions.
diff --git a/src/main/java/com/gildedrose/foundation/lenses.kt b/src/main/java/com/gildedrose/foundation/lenses.kt
@@ -12,6 +12,11 @@ interface Lens<T, R> : (T) -> R {
     operator fun invoke(subject: T, value: R): T = inject(subject, value)
 }
 
+
+infix fun <T1, T2, R> ((T1) -> T2?).andThen(second: (T2) -> R): (T1) -> R? = {
+    this.invoke(it)?.let { outer -> second.invoke(outer) }
+}
+
 infix fun <T1, T2, R> Lens<T1, T2>.andThen(second: Lens<T2, R>): Lens<T1, R> = LensObject(
     { second.get(get(it)) },
     { subject, value ->
@@ -23,13 +28,13 @@ infix fun <T1, T2, R> Lens<T1, T2>.andThen(second: Lens<T2, R>): Lens<T1, R> = L
 )
 
 @JvmName("andThenMaybe")
-infix fun <T1, T2, R> Lens<T1, T2?>.andThen(second: Lens<T2, R>): Lens<T1, R?> = LensObject(
+infix fun <T1, T2, R> Lens<T1, T2?>.andThen(second: Lens<T2, R?>): Lens<T1, R?> = LensObject(
     getter = { get(it)?.let { outer -> second.get(outer) } },
     injector = { subject, value ->
         val outer = get(subject) ?: error("No parent found to inject into")
         inject(
             subject,
-            second.inject(outer, value ?: error("Cannot remove the parent to inject null"))
+            second.inject(outer, value)
         )
     }
 )

diff --git a/src/test/java/com/gildedrose/competition/CompetitionTests.kt b/src/test/java/com/gildedrose/competition/CompetitionTests.kt
@@ -69,17 +69,32 @@ class CompetitionTests {
         expectThat(reverted).isEqualTo(mapOf("propertyName" to null))
     }
 
+    @Test
+    fun `chaining nullable functions`() {
+        val lens: (PropertySet) -> String? = lens<PropertySet?>("outer") andThen "inner".asLens<String>()
+
+        val populatedData = mapOf("outer" to mapOf("inner" to "value"))
+        expectThat(populatedData[lens]).isEqualTo("value")
+
+        val emptyData = mapOf<String, Any?>()
+        expectThat(emptyData[lens]).isNull()
+
+        val outerButNoInner = mapOf("outer" to emptyData)
+        expectThrows<NoSuchElementException> { outerButNoInner[lens] }
+    }
+
     @Test
     fun `chaining nullable lenses`() {
-        val lens: Lens<PropertySet, String?> = lens<PropertySet?>("outer") andThen "inner".asLens<String>()
+        val lens: Lens<PropertySet, String?> = lens<PropertySet?>("outer") andThen "inner".asLens<String?>()
 
         val populatedData = mapOf("outer" to mapOf("inner" to "value"))
         expectThat(populatedData[lens]).isEqualTo("value")
         expectThat(populatedData.with(lens, "new value")).isEqualTo(
             mapOf("outer" to mapOf("inner" to "new value"))
         )
-        expectThrows<IllegalStateException> { populatedData.with(lens, null) }
-            .message.isEqualTo("Cannot remove the parent to inject null")
+        expectThat(populatedData.with(lens, null)).isEqualTo(
+            mapOf("outer" to mapOf("inner" to null))
+        )
 
         val emptyData = mapOf<String, Any?>()
         expectThat(emptyData[lens]).isNull()
@@ -89,12 +104,13 @@ class CompetitionTests {
             .message.isEqualTo("No parent found to inject into")
 
         val outerButNoInner = mapOf("outer" to emptyData)
-        expectThrows<NoSuchElementException> { outerButNoInner[lens] }
+        expectThat(outerButNoInner[lens]).isEqualTo(null)
         expectThat(outerButNoInner.with(lens, "value")).isEqualTo(
             mapOf("outer" to mapOf("inner" to "value"))
         )
-        expectThrows<IllegalStateException> { outerButNoInner.with(lens, null) }
-            .message.isEqualTo("Cannot remove the parent to inject null")
+        expectThat(outerButNoInner.with(lens, null)).isEqualTo(
+            mapOf("outer" to mapOf("inner" to null))
+        )
     }
 
     data class Place(val properties: PropertySet) : PropertySet by properties {