From 0d5d3039cfe0c0685bca8877078c46da1a0fc618 Mon Sep 17 00:00:00 2001
From: Denis Zhdanov <denzhdanov@gmail.com>
Date: Sun, 25 Nov 2018 13:53:48 +0800
Subject: [PATCH] BAEL-2373 Kotlin Contracts

* upgraded kotlin version to 1.3.10
* added contract examples
---
 .../baeldung/contract/CallsInPlaceEffect.kt   | 23 ++++++++++
 .../com/baeldung/contract/ReturnsEffect.kt    | 43 +++++++++++++++++++
 parent-kotlin/pom.xml                         |  2 +-
 3 files changed, 67 insertions(+), 1 deletion(-)
 create mode 100644 core-kotlin/src/main/kotlin/com/baeldung/contract/CallsInPlaceEffect.kt
 create mode 100644 core-kotlin/src/main/kotlin/com/baeldung/contract/ReturnsEffect.kt

diff --git a/core-kotlin/src/main/kotlin/com/baeldung/contract/CallsInPlaceEffect.kt b/core-kotlin/src/main/kotlin/com/baeldung/contract/CallsInPlaceEffect.kt
new file mode 100644
index 0000000000..ca0b13cdc7
--- /dev/null
+++ b/core-kotlin/src/main/kotlin/com/baeldung/contract/CallsInPlaceEffect.kt
@@ -0,0 +1,23 @@
+package com.baeldung.contract
+
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
+
+@ExperimentalContracts
+inline fun <R> myRun(block: () -> R): R {
+    contract {
+        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
+    }
+    return block()
+}
+
+@ExperimentalContracts
+fun callsInPlace() {
+    val i: Int
+    myRun {
+        i = 1 // Without contract initialization is forbidden due to possible re-assignment
+    }
+    println(i) // Without contract variable might be uninitialized
+}
+
diff --git a/core-kotlin/src/main/kotlin/com/baeldung/contract/ReturnsEffect.kt b/core-kotlin/src/main/kotlin/com/baeldung/contract/ReturnsEffect.kt
new file mode 100644
index 0000000000..56f667af82
--- /dev/null
+++ b/core-kotlin/src/main/kotlin/com/baeldung/contract/ReturnsEffect.kt
@@ -0,0 +1,43 @@
+package com.baeldung.contract
+
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
+
+data class Request(val arg: String)
+
+class Service {
+
+    @ExperimentalContracts
+    fun process(request: Request?) {
+        validate(request)
+        println(request.arg)
+    }
+
+}
+
+@ExperimentalContracts
+private fun validate(request: Request?) {
+    contract {
+        returns() implies (request != null)
+    }
+    if (request == null) {
+        throw IllegalArgumentException("Undefined request")
+    }
+}
+
+data class MyEvent(val message: String)
+
+@ExperimentalContracts
+fun processEvent(event: Any?) {
+    if (isInterested(event)) {
+        println(event.message) // Compiler makes smart cast here with the help of contract
+    }
+}
+
+@ExperimentalContracts
+fun isInterested(event: Any?): Boolean {
+    contract {
+        returns(true) implies (event is MyEvent)
+    }
+    return event is MyEvent
+}
\ No newline at end of file
diff --git a/parent-kotlin/pom.xml b/parent-kotlin/pom.xml
index f8283bd920..73c98e1a80 100644
--- a/parent-kotlin/pom.xml
+++ b/parent-kotlin/pom.xml
@@ -202,7 +202,7 @@
 	</build>
 
 	<properties>
-		<kotlin.version>1.3.0</kotlin.version>
+		<kotlin.version>1.3.10</kotlin.version>
 		<kotlinx.version>1.0.0</kotlinx.version>
 		<ktor.io.version>0.9.5</ktor.io.version>
 		<assertj.version>3.11.0</assertj.version>