Delegates.mapVal and mapVar preserve type of the receiver to when calling default value lambda.

libraries/stdlib/src/kotlin/properties/Delegation.kt

@@ -55,9 +55,9 @@ public object Delegates {
      * @param map the map where the property values are stored.
      * @param default the function returning the value of the property for a given object if it's missing from the given map.
      */
-    public fun <T> mapVar(map: MutableMap<in String, Any?>,
-                          default: (thisRef: Any?, desc: String) -> T): ReadWriteProperty<Any?, T> {
-        return FixedMapVar<Any?, String, T>(map, propertyNameSelector, default)
+    public fun <R, T> mapVar(map: MutableMap<in String, Any?>,
+                             default: (thisRef: R, propertyName: String) -> T): ReadWriteProperty<R, T> {
+        return FixedMapVar<R, String, T>(map, propertyNameSelector, default)
     }
 
     /**
@@ -76,9 +76,9 @@ public object Delegates {
      * @param map the map where the property values are stored.
      * @param default the function returning the value of the property for a given object if it's missing from the given map.
      */
-    public fun <T> mapVal(map: Map<in String, Any?>,
-                          default: (thisRef: Any?, desc: String) -> T): ReadOnlyProperty<Any?, T> {
-        return FixedMapVal<Any?, String, T>(map, propertyNameSelector, default)
+    public fun <R, T> mapVal(map: Map<in String, Any?>,
+                             default: (thisRef: R, propertyName: String) -> T): ReadOnlyProperty<R, T> {
+        return FixedMapVal<R, String, T>(map, propertyNameSelector, default)
     }
 }
 

libraries/stdlib/test/properties/delegation/MapDelegationTest.kt

@@ -8,6 +8,7 @@ import kotlin.test.*
 
 data class B(val a: Int)
 
+
 class MapValWithDifferentTypesTest() {
     val map = hashMapOf("a" to "a", "b" to 1, "c" to B(1), "d" to null)
     val a by Delegates.mapVal<String>(map)
@@ -75,11 +76,13 @@ class MapValWithDefaultTest() {
     val a: String by Delegates.mapVal(map, default = { ref, desc -> "aDefault" })
     val b: String by FixedMapVal(map, default = { ref: MapValWithDefaultTest, desc: String -> "bDefault" }, key = {"b"})
     val c: String by FixedMapVal(map, default = { ref: MapValWithDefaultTest, desc: String -> "cDefault" }, key = { desc -> desc.name })
+    val d: String by Delegates.mapVal(map, default = { ref, name -> ref.c })
 
     @test fun doTest() {
-        assertTrue(a == "aDefault", "fail at 'a'")
-        assertTrue(b == "bDefault", "fail at 'b'")
-        assertTrue(c == "cDefault", "fail at 'c'")
+        assertEquals("aDefault", a, "fail at 'a'")
+        assertEquals("bDefault", b, "fail at 'b'")
+        assertEquals("cDefault", c, "fail at 'c'")
+        assertEquals(c, d, "'d' must have the default value equal to 'c'")
     }
 }
 
@@ -88,17 +91,20 @@ class MapVarWithDefaultTest() {
     var a: String by Delegates.mapVar(map, default = {ref, desc -> "aDefault" })
     var b: String by FixedMapVar(map, default = {ref: Any?, desc: String -> "bDefault" }, key = {"b"})
     var c: String by FixedMapVar(map, default = {ref: Any?, desc: String -> "cDefault" }, key = { desc -> desc.name })
+    var d: String by Delegates.mapVar(map, default = { ref, name -> ref.c })
 
     @test fun doTest() {
-        assertTrue(a == "aDefault", "fail at 'a'")
-        assertTrue(b == "bDefault", "fail at 'b'")
-        assertTrue(c == "cDefault", "fail at 'c'")
+        assertEquals("aDefault", a, "fail at 'a'")
+        assertEquals("bDefault", b, "fail at 'b'")
+        assertEquals("cDefault", c, "fail at 'c'")
+        assertEquals(c, d, "'d' must have the default value equal to 'c'")
         a = "a"
         b = "b"
         c = "c"
-        assertTrue(a == "a", "fail at 'a' after set")
-        assertTrue(b == "b", "fail at 'b' after set")
-        assertTrue(c == "c", "fail at 'c' after set")
+        assertEquals("a", a, "fail at 'a' after set")
+        assertEquals("b", b, "fail at 'b' after set")
+        assertEquals("c", c, "fail at 'c' after set")
+        assertEquals(c, d, "'d' must still have the default value equal to 'c'")
     }
 }
 
@@ -126,6 +132,15 @@ class MapPropertyFunctionTest() {
     }
 }
 
+@Suppress("ALWAYS_NULL")
+private val topLevel: String by Delegates.mapVal(emptyMap(), default = { ref, name -> ref.toString() })
+
+class MapTopLevelVarWithDefaultTest() {
+    @test fun doTest() {
+        assertEquals("null", topLevel)
+    }
+}
+
 val mapVal = object : MapVal<MapPropertyCustomTest, String, String>() {
     override fun map(ref: MapPropertyCustomTest) = ref.map
     override fun key(property: KProperty<*>) = "${property.name}Desc"
@@ -152,14 +167,14 @@ val mapValWithDefault = object : MapVal<MapPropertyCustomWithDefaultTest, String
     override fun map(ref: MapPropertyCustomWithDefaultTest) = ref.map
     override fun key(property: KProperty<*>) = property.name
 
-    override fun default(ref: MapPropertyCustomWithDefaultTest, key: KProperty<*>) = "default"
+    override fun default(ref: MapPropertyCustomWithDefaultTest, property: KProperty<*>) = "default"
 }
 
 val mapVarWithDefault = object : MapVar<MapPropertyCustomWithDefaultTest, String, String>() {
     override fun map(ref: MapPropertyCustomWithDefaultTest) = ref.map
     override fun key(property: KProperty<*>) = property.name
 
-    override fun default(ref: MapPropertyCustomWithDefaultTest, key: KProperty<*>) = "default"
+    override fun default(ref: MapPropertyCustomWithDefaultTest, property: KProperty<*>) = "default"
 }
 
 class MapPropertyCustomWithDefaultTest() {