From a1736892495c348cef7cceea5fc468a98b160e88 Mon Sep 17 00:00:00 2001
From: green-nick <paul.grynyk@gmail.com>
Date: Wed, 23 Oct 2019 11:08:21 +0300
Subject: [PATCH]  - create mapNotNull mapper;  - update README;

---
 README.md                                     | 12 +++++
 .../properties/generic/PropertiesExt.kt       | 13 +++++
 .../generic/PropertiesMappingTest.kt          | 48 +++++++++++++++++++
 3 files changed, 73 insertions(+)

diff --git a/README.md b/README.md
index b12e946..5e41e32 100644
--- a/README.md
+++ b/README.md
@@ -127,6 +127,18 @@ val property = propertyOf("Hello")
 val length: MutableProperty<Int> = property.map { it.length } // will contain 5
 ```
 Also notice that mapped value will be triggered on all updates of origin one.
+
+Besides that, there is mapper for nullable properties:
+```
+val origin = propertyOf<String?>(null)
+
+val length: MutableProperty<Int> = property.mapNotNull(0) { it.length } // will contain 0
+
+origin.value = "hello"
+length.value == 5
+```
+If init value of origin property is `null`, default value will be used for initialization.  
+All non-null set values will be mapped.
 #### Addition:
 You can add two different properties and get new one and receive all updates pushed to origins as Pair of their values:
 ```
diff --git a/src/main/java/com/github/greennick/properties/generic/PropertiesExt.kt b/src/main/java/com/github/greennick/properties/generic/PropertiesExt.kt
index 5003093..3fc0df0 100644
--- a/src/main/java/com/github/greennick/properties/generic/PropertiesExt.kt
+++ b/src/main/java/com/github/greennick/properties/generic/PropertiesExt.kt
@@ -54,6 +54,19 @@ fun <T, R> Property<T>.map(mapper: (T) -> R): MutableProperty<R> {
     return new
 }
 
+fun <T, R> Property<T?>.mapNotNull(default: R, mapper: (T) -> R): MutableProperty<R> {
+    val init = this.value
+    val new = if (init == null) {
+        propertyOf(default)
+    } else {
+        propertyOf(mapper(init))
+    }
+
+    this.subscribe { new.value = mapper(it ?: return@subscribe) }
+
+    return new
+}
+
 fun <T1, T2, E> Property<T1>.zipWith(another: Property<T2>, zipper: (T1, T2) -> E): MutableProperty<E> {
     val new = propertyOf(zipper(this.value, another.value))
 
diff --git a/src/test/java/com/github/greennick/properties/generic/PropertiesMappingTest.kt b/src/test/java/com/github/greennick/properties/generic/PropertiesMappingTest.kt
index 26f1e00..bdbd681 100644
--- a/src/test/java/com/github/greennick/properties/generic/PropertiesMappingTest.kt
+++ b/src/test/java/com/github/greennick/properties/generic/PropertiesMappingTest.kt
@@ -26,4 +26,52 @@ class PropertiesMappingTest {
 
         assert(mapped.value == newValue.length)
     }
+
+    @Test
+    fun `property got default instead of mapped null value`() {
+        val default = 2
+
+        val origin = propertyOf<String?>(null)
+        val mapped = origin.mapNotNull(default) { it.length }
+
+        assert(mapped.value == default)
+    }
+
+    @Test
+    fun `property got nonnull mapped value`() {
+        val default = 0
+        val initValue = "hello"
+
+        val origin = propertyOf<String?>(initValue)
+        val mapped = origin.mapNotNull(default) { it.length }
+
+        assert(mapped.value == initValue.length)
+        assert(mapped.value != default)
+    }
+
+    @Test
+    fun `mapped property receive updated nonnull value`() {
+        val default = 0
+        val origin = propertyOf<String?>("hello")
+
+        val mapped = origin.mapNotNull(default) { it.length }
+
+        val newValue = "worlds!!!"
+        origin.value = newValue
+
+        assert(mapped.value == newValue.length)
+    }
+
+    @Test
+    fun `mapped property doesn't receive updated nullable value`() {
+        val default = 0
+        val init = "hello"
+        val origin = propertyOf<String?>(init)
+
+        val mapped = origin.mapNotNull(default) { it.length }
+
+        origin.value = null
+
+        assert(mapped.value == init.length)
+    }
 }
\ No newline at end of file