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Lysanderchristian.hausknecht
Lysander
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christian.hausknecht
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Improves support for upcasting lenses (#925)
Introduces a dedicated `Lens`-factory fpr upcasting lenses: `lensForUpcasting` Its inner code will catch `ClassCastException`s, which can occur in nested `Mountpoints`, and throw a dedicated `CollectionLensGetException`. This solution is similar to the handling of false index access or access by keys for collections, we already have integrated. This is necessary due to the fact, that fritz2 does not maintain any sort of `Flow`-hierarchie from the outermost to the innermost renderings. So the framework cannot control the sequence of collecting the involved flows, in order to prevent outdated data or - for this case - *types*. This is a practical compromise, that will work very well for UIs, as the visual appearance is kind of *dictated* by the properties of the underlying type. Co-authored-by: christian.hausknecht <christian.hausknecht@oeffentliche.de>
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‎core/src/commonMain/kotlin/dev/fritz2/core/Lens.kt‎

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@@ -178,6 +178,15 @@ fun <K, V> lensForElement(key: K): Lens<Map<K, V>, V> = object : Lens<Map<K, V>,
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else throw CollectionLensSetException("no item found with key='$key'")
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}
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/**
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* create a [Lens] for upcasting a base (sealed) class or interface to a specific subtype.
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*/
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inline fun <P, reified C : P> lensForUpcasting(): Lens<P, C> = object : Lens<P, C> {
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override val id: String = ""
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override fun get(parent: P): C = (parent as? C) ?: throw CollectionLensGetException()
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override fun set(parent: P, value: C): P = value
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}
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/**
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* Creates a lens from a nullable parent to a non-nullable value using a given default-value.
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* Use this method to apply a default value that will be used in the case that the real value is null.

‎core/src/commonTest/kotlin/dev/fritz2/core/Lens.kt‎

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@@ -103,4 +103,30 @@ class LensesTests {
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"not null lens does not throw exception when set on null parent"
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) { notNullLens.set(null, newValue)?.street }
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}
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sealed interface ConsultationModel {
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val stockNumber: String
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data class Agency(override val stockNumber: String, val branch: String) : ConsultationModel
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data class Private(override val stockNumber: String) : ConsultationModel
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}
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@Test
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fun lensForUpcasting_withSuitableSubtypeTarget_willGetSubtype() {
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val agency: ConsultationModel = ConsultationModel.Agency("123", "woodworking")
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val sut = lensForUpcasting<ConsultationModel, ConsultationModel.Agency>()
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val result = sut.get(agency)
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assertEquals(agency, result)
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}
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@Test
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fun lensForUpcasting_withInvalidTarget_willThrow() {
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val agency: ConsultationModel = ConsultationModel.Agency("123", "woodworking")
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val sut = lensForUpcasting<ConsultationModel, ConsultationModel.Private>()
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assertFailsWith<CollectionLensGetException> { sut.get(agency) }
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}
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}

‎lenses-annotation-processor/src/jvmMain/kotlin/dev/fritz2/lens/LensesProcessor.kt‎

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@@ -265,14 +265,9 @@ private class LensesVisitor(
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.receiver(compObj.asType(emptyList()).toTypeName())
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.apply {
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addCode(
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"""
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|return %M(
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| "",
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| { it as %T },
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| { _, v -> v }
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|)
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""".trimMargin(),
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MemberName("dev.fritz2.core", "lensOf"),
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"return %M<%T,%T>()",
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MemberName("dev.fritz2.core", "lensForUpcasting"),
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classDeclaration.toClassName(),
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child.toClassName(),
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)
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}

‎lenses-annotation-processor/src/jvmTest/kotlin/dev/fritz2/lens/LensesProcessorTests.kt‎

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@@ -124,6 +124,7 @@ class LensesProcessorTests {
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|package dev.fritz2.lenstest
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|
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|import dev.fritz2.core.Lens
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|import dev.fritz2.core.lensForUpcasting
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|import dev.fritz2.core.lensOf
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|import kotlin.Int
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|
@@ -143,11 +144,7 @@ class LensesProcessorTests {
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|
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|public fun <PARENT> Lens<PARENT, Bar>.bar(): Lens<PARENT, Int> = this + Bar.bar()
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|
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|public fun Bar.Companion.barImpl(): Lens<Bar, BarImpl> = lensOf(
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| "",
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| { it as BarImpl },
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| { _, v -> v }
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|)
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|public fun Bar.Companion.barImpl(): Lens<Bar, BarImpl> = lensForUpcasting<Bar,BarImpl>()
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""".trimMargin()
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)
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}
@@ -581,6 +578,7 @@ class LensesProcessorTests {
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|package dev.fritz2.lenstest
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|
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|import dev.fritz2.core.Lens
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|import dev.fritz2.core.lensForUpcasting
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|import dev.fritz2.core.lensOf
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|import kotlin.Int
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|import kotlin.String
@@ -659,17 +657,11 @@ class LensesProcessorTests {
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|public fun <PARENT> Lens<PARENT, Framework>.baz(): Lens<PARENT, MyGenericType<Int>> = this +
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| Framework.baz()
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|
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|public fun Framework.Companion.fritz2(): Lens<Framework, Fritz2> = lensOf(
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| "",
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| { it as Fritz2 },
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| { _, v -> v }
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|)
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|public fun Framework.Companion.fritz2(): Lens<Framework, Fritz2> =
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| lensForUpcasting<Framework,Fritz2>()
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|
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|public fun Framework.Companion.spring(): Lens<Framework, Spring> = lensOf(
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| "",
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| { it as Spring },
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| { _, v -> v }
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|)
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|public fun Framework.Companion.spring(): Lens<Framework, Spring> =
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| lensForUpcasting<Framework,Spring>()
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""".trimMargin()
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@JvmStatic
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|package dev.fritz2.lenstest
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|
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|import dev.fritz2.core.Lens
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|import dev.fritz2.core.lensOf
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|import dev.fritz2.core.lensForUpcasting
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|
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|public fun Foo.Companion.fooImpl(): Lens<Foo, FooImpl> = lensOf(
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| "",
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| { it as FooImpl },
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| { _, v -> v }
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|)
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|public fun Foo.Companion.fooImpl(): Lens<Foo, FooImpl> = lensForUpcasting<Foo,FooImpl>()
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""".trimMargin()
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),
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arguments(
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|package dev.fritz2.lenstest
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|
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|import dev.fritz2.core.Lens
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|import dev.fritz2.core.lensOf
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|import dev.fritz2.core.lensForUpcasting
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|
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|public fun Foo.Companion.fooImpl(): Lens<Foo, FooImpl> = lensOf(
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| "",
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| { it as FooImpl },
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| { _, v -> v }
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|)
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|public fun Foo.Companion.fooImpl(): Lens<Foo, FooImpl> = lensForUpcasting<Foo,FooImpl>()
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""".trimMargin()
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),
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)
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|package dev.fritz2.lenstest
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|
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|import dev.fritz2.core.Lens
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|import dev.fritz2.core.lensForUpcasting
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|import dev.fritz2.core.lensOf
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|import kotlin.String
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|
@@ -1376,17 +1361,11 @@ class LensesProcessorTests {
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|
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|public fun <PARENT> Lens<PARENT, Framework>.foo(): Lens<PARENT, String> = this + Framework.foo()
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|
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|public fun Framework.Companion.fritz2(): Lens<Framework, Fritz2> = lensOf(
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| "",
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| { it as Fritz2 },
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| { _, v -> v }
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|)
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|public fun Framework.Companion.fritz2(): Lens<Framework, Fritz2> =
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| lensForUpcasting<Framework,Fritz2>()
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|
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|public fun Framework.Companion.spring(): Lens<Framework, Spring> = lensOf(
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| "",
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| { it as Spring },
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| { _, v -> v }
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|)
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|public fun Framework.Companion.spring(): Lens<Framework, Spring> =
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| lensForUpcasting<Framework,Spring>()
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""".trimMargin()
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‎www/src/pages/docs/50_StoreMapping.md‎

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@@ -412,13 +412,14 @@ Take a look at our complete [validation example](/examples/validation) to get an
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### Summary Lens-Factories
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| Factory | Use case |
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|---------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------|
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| `lensOf(id: String, getter: (P) -> T, setter: (P, T) -> P): Lens<P, T>` | Most generic lens (used by `lenses-annotation-processor`. Fits for complex model destructuring. |
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| `lensOf(parse: (String) -> P, format: (P) -> String): Lens<P, String>` | Formatting lens: Use for mapping into `String`s. |
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| `lensForElement(element: T, idProvider: IdProvider<T, I>): Lens<List, T>` | Select one element from a list of entities, therefore a stable Id is needed. |
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| `lensForElement(index: Int): Lens<List, T>` | Select one element from a list by index. Useful for value objects. |
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| `lensForElement(key: K): Lens<Map<K, V>, V>` | Select one element from a map by key. |
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| Factory | Use case |
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|---------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------|
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| `lensOf(id: String, getter: (P) -> T, setter: (P, T) -> P): Lens<P, T>` | Most generic lens (used by `lenses-annotation-processor`. Fits for complex model destructuring. |
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| `lensOf(parse: (String) -> P, format: (P) -> String): Lens<P, String>` | Formatting lens: Use for mapping into `String`s. |
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| `lensForElement(element: T, idProvider: IdProvider<T, I>): Lens<List, T>` | Select one element from a list of entities, therefore a stable Id is needed. |
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| `lensForElement(index: Int): Lens<List, T>` | Select one element from a list by index. Useful for value objects. |
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| `lensForElement(key: K): Lens<Map<K, V>, V>` | Select one element from a map by key. |
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| `lensForUpcasting(): Lens<Map<P, C>` | Casting lens: Interpret parent as specific subtype. Handles `ClassCastException` for render edge-cases |
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## Advanced Topics
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@@ -639,6 +640,14 @@ Casting from the base type to a more specific type is called up-casting.
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Since we apply this to a lens, we call this kind of lens *up-casting* lens.
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:::
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But beware that the above code behaves still a bit brittle, as we do not cope with casting problems!
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That's why fritz2 offers a dedicated lens factory for this use case: `lensForUpcasting`:
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```kotlin
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val computerLens: Lens<Wish, Computer> = lensForUpcasting<Wish, Computer>()
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```
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Our automatic lens generator relies on this factory too. So strive to use this, if you craft your up-casting lenses
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manually.
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Armed with such an up-casting lenses, we can easily access or change values of our example `WishList`-object:
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```kotlin
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val wishlist = Wishlist(
@@ -649,11 +658,7 @@ val wishlist = Wishlist(
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)
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)
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val upcastingLens: Lens<Wish, Computer> = lensOf(
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"",
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{ it as Computer },
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{ _, v -> v }
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)
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val upcastingLens: Lens<Wish, Computer> = lensForUpcasting<Wish, Computer>()
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// craft a lens to access the `Computer.raminKb`-property from a `WishList` by combining the
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// intermediate lenses by `+`-operator:

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