1) fromFileOrNull 2) ifNot

gradle/wrapper/gradle-wrapper.properties

@@ -1,4 +1,4 @@
-#Fri Apr 21 08:48:38 BST 2017
+#Wed Feb 07 19:56:24 MSK 2018
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME

src/main/kotlin/com/natpryce/konfig/konfig.kt

@@ -184,11 +184,20 @@ class ConfigurationProperties(
         }
 
          /**
-         * Load from optional file
+         * Load from optional file, returns EmptyConfiguration if file is not found
          */
         @JvmStatic
-        fun fromOptionalFile(file: File) = if (file.exists()) fromFile(file) else EmptyConfiguration
-
+        fun fromFileOrEmpty(file: File) = if (file.exists()) fromFile(file) else EmptyConfiguration
+
+
+        /**
+         * Load from optional file, returns EmptyConfiguration if file is not found
+         */
+        @JvmStatic
+        fun fromFileOrNull(file: File) = if (file.exists()) fromFile(file) else null
+
+
+
         private fun load(input: InputStream?, location: Location, errorMessageFn: () -> String) =
             (input ?: throw Misconfiguration(errorMessageFn())).use {
                 ConfigurationProperties(Properties().apply { load(input) }, location)
@@ -291,6 +300,9 @@ class Override(
 
 infix fun Configuration.overriding(defaults: Configuration?) = if (defaults == null) this else Override(this, defaults)
 
+infix fun Configuration.ifNot(betterConf: Configuration?) = betterConf ?: this
+
+
 fun search(first: Configuration, vararg rest: Configuration) = rest.fold(first, ::Override)
 
 /**

src/test/kotlin/com/natpryce/konfig/konfig_tests.kt

@@ -8,6 +8,7 @@ import org.junit.Test
 import java.io.File
 import java.util.*
 import kotlin.test.assertFalse
+import kotlin.test.assertNull
 import kotlin.test.assertTrue
 
 
@@ -153,10 +154,24 @@ class OverridingAndFallingBack {
 
     val config = overrides overriding defaults
 
+    val sosoConfig = defaults ifNot null
+    val bestConfig = defaults ifNot overrides
+
     val x = Key("x", stringType)
     val y = Key("y", stringType)
     val z = Key("z", stringType)
 
+    @Test
+    fun overrides_properties_if_not() {
+        assertThat(sosoConfig[x], equalTo("x"))
+        assertThat(sosoConfig[y], equalTo("y"))
+
+        assertThat(bestConfig[x], equalTo("XX"))
+        assertFalse(bestConfig.contains(y))
+        assertThat(bestConfig[z], equalTo("ZZ"))
+    }
+
+
     @Test
     fun overrides_default_properties() {
         assertThat(config[x], equalTo("XX"))
@@ -298,6 +313,14 @@ class FromResources {
         assertThat(config[a], equalTo(1))
         assertThat(config[b], equalTo("two"))
     }
+}
+
+
+class FromFile {
+
+    val a = Key("a", intType)
+    val b = Key("b", stringType)
+
 
     @Test
     fun can_load_from_file() {
@@ -306,19 +329,35 @@ class FromResources {
         assertThat(config[a], equalTo(1))
         assertThat(config[b], equalTo("two"))
     }
-    
+
     @Test
     fun can_load_from_optional_file() {
-        val config = ConfigurationProperties.fromOptionalFile(File("src/test/resources/com/natpryce/konfig/example.properties"))
+        val config = ConfigurationProperties.fromFileOrEmpty(File("src/test/resources/com/natpryce/konfig/example.properties"))
 
         assertThat(config[a], equalTo(1))
         assertThat(config[b], equalTo("two"))
     }
 
     @Test
     fun should_return_empty_config_when_load_from_optional_file_thats_not_present() {
-        val config = ConfigurationProperties.fromOptionalFile(File("not.available.file"))
+        val config = ConfigurationProperties.fromFileOrEmpty(File("not.available.file"))
 
         assertThat(config, equalTo<Configuration>(EmptyConfiguration))
-    }    
+    }
+
+
+    @Test
+    fun can_load_from_optional_file_2() {
+        val config = ConfigurationProperties.fromFileOrNull(File("src/test/resources/com/natpryce/konfig/example.properties")) ?: throw NullPointerException("Config should be loaded")
+
+        assertThat(config[a], equalTo(1))
+        assertThat(config[b], equalTo("two"))
+    }
+
+    @Test
+    fun should_return_null_when_load_from_optional_file_thats_not_present() {
+        val config = ConfigurationProperties.fromFileOrNull(File("not.available.file"))
+
+        assertNull(config)
+    }
 }