Chaining nullable lenses

dmcg · Dec 30, 2023 · 66bd0b4 · 66bd0b4
1 parent 6f525cd
commit 66bd0b4
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Showing 3 changed files with 51 additions and 7 deletions.
diff --git a/src/main/java/com/gildedrose/foundation/PropertySet.kt b/src/main/java/com/gildedrose/foundation/PropertySet.kt
@@ -17,15 +17,15 @@ inline fun <reified T> PropertySet.valueOf(key: String): T =
 
 object PropertySets {
     @JvmName("lensPropertySet")
-    fun lens(propertyName: String) = lens<PropertySet>(propertyName)
+    fun lens(propertyName: String): Lens<PropertySet, PropertySet> = lens<PropertySet>(propertyName)
 
     @JvmName("aslensPropertySet")
-    fun String.asLens() = lens(this)
+    fun String.asLens(): Lens<PropertySet, PropertySet> = lens(this)
 
-    inline fun <reified R> String.asLens() = lens<R>(this)
+    inline fun <reified R> String.asLens(): Lens<PropertySet, R> = lens<R>(this)
 
-    inline fun <reified R> lens(propertyName: String) =
-        LensObject<PropertySet, R>(
+    inline fun <reified R> lens(propertyName: String): Lens<PropertySet, R> =
+        LensObject(
             getter = { it.valueOf<R>(propertyName) },
             injector = { subject, value ->
                 subject.toMutableMap().apply {

diff --git a/src/main/java/com/gildedrose/foundation/lenses.kt b/src/main/java/com/gildedrose/foundation/lenses.kt
@@ -12,7 +12,7 @@ interface Lens<T, R> : (T) -> R {
     operator fun invoke(subject: T, value: R): T = inject(subject, value)
 }
 
-infix fun <T1, T2, R> LensObject<T1, T2>.andThen(second: LensObject<T2, R>) = LensObject<T1, R>(
+infix fun <T1, T2, R> Lens<T1, T2>.andThen(second: Lens<T2, R>): Lens<T1, R> = LensObject(
     { second.get(get(it)) },
     { subject, value ->
         inject(
@@ -22,6 +22,18 @@ infix fun <T1, T2, R> LensObject<T1, T2>.andThen(second: LensObject<T2, R>) = Le
     }
 )
 
+@JvmName("andThenMaybe")
+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"))
+        )
+    }
+)
+
 operator fun <T: Any, R> T.get(extractor: (T) -> R) = extractor(this)
 fun <T: Any, R> T.with(lens: Lens<T, R>, of: R) = lens.inject(this, of)
 fun <T: Any, R> T.updatedWith(lens: Lens<T, R>, f: (R) -> R) = lens.update(this, f)
@@ -34,7 +46,7 @@ data class LensObject<T, R>(
     override fun inject(subject: T, value: R) = injector(subject, value)
 }
 
-inline fun <reified T: Any, R> KProperty1<T, R>.asLens(): LensObject<T, R> = LensObject(
+inline fun <reified T: Any, R> KProperty1<T, R>.asLens(): Lens<T, R> = LensObject(
     ::get,
     reflectiveCopy(name)
 )

diff --git a/src/test/java/com/gildedrose/competition/CompetitionTests.kt b/src/test/java/com/gildedrose/competition/CompetitionTests.kt
@@ -5,6 +5,7 @@ import com.fasterxml.jackson.module.kotlin.readValue
 import com.gildedrose.competition.FetchData.Companion.dataFile
 import com.gildedrose.foundation.*
 import com.gildedrose.foundation.PropertySets.asLens
+import com.gildedrose.foundation.PropertySets.lens
 import org.http4k.testing.ApprovalTest
 import org.http4k.testing.Approver
 import org.http4k.testing.assertApproved
@@ -14,6 +15,7 @@ import strikt.api.expectThat
 import strikt.api.expectThrows
 import strikt.assertions.isEqualTo
 import strikt.assertions.isNull
+import strikt.assertions.message
 
 @ExtendWith(ApprovalTest::class)
 class CompetitionTests {
@@ -67,6 +69,34 @@ class CompetitionTests {
         expectThat(reverted).isEqualTo(mapOf("propertyName" to null))
     }
 
+    @Test
+    fun `chaining nullable lenses`() {
+        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")
+
+        val emptyData = mapOf<String, Any?>()
+        expectThat(emptyData[lens]).isNull()
+        expectThrows<IllegalStateException> { emptyData.with(lens, "value") }
+            .message.isEqualTo("No parent found to inject into")
+        expectThrows<IllegalStateException> { emptyData.with(lens, null) }
+            .message.isEqualTo("No parent found to inject into")
+
+        val outerButNoInner = mapOf("outer" to emptyData)
+        expectThrows<NoSuchElementException> { outerButNoInner[lens] }
+        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")
+    }
+
     data class Place(val properties: PropertySet) : PropertySet by properties {
         private val displayNameTextLens = "displayName".asLens() andThen "text".asLens<String>()
         private val addressComponents get() = valueOf<List<PropertySet>>("addressComponents").map(::AddressComponent)
@@ -83,3 +113,5 @@ class CompetitionTests {
         val types = valueOf<List<String>>("types")
     }
 }
+
+