BAEL-2650 - Kotlin standard functions: run, with, let, also and apply (#6553)

core-kotlin-2/src/main/kotlin/com/baeldung/scope/ScopeFunctions.kt

@@ -0,0 +1,25 @@
+package com.baeldung.scope
+
+data class Student(var studentId: String = "", var name: String = "", var surname: String = "") {
+}
+
+data class Teacher(var teacherId: Int = 0, var name: String = "", var surname: String = "") {
+    fun setId(anId: Int): Teacher = apply { teacherId = anId }
+    fun setName(aName: String): Teacher = apply { name = aName }
+    fun setSurname(aSurname: String): Teacher = apply { surname = aSurname }
+}
+
+data class Headers(val headerInfo: String)
+
+data class Response(val headers: Headers)
+
+data class RestClient(val url: String) {
+    fun getResponse() = Response(Headers("some header info"))
+}
+
+data class BankAccount(val id: Int) {
+    fun checkAuthorization(username: String) = Unit
+    fun addPayee(payee: String) = Unit
+    fun makePayment(paymentDetails: String) = Unit
+
+}

core-kotlin-2/src/test/kotlin/com/baeldung/scope/ScopeFunctionsUnitTest.kt

@@ -0,0 +1,119 @@
+package com.baeldung.scope
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+
+class ScopeFunctionsUnitTest {
+
+    class Logger {
+
+        var called : Boolean = false
+
+        fun info(message: String) {
+            called = true
+        }
+
+        fun wasCalled() = called
+    }
+
+    @Test
+    fun shouldTransformWhenLetFunctionUsed() {
+        val stringBuider = StringBuilder()
+        val numberOfCharacters = stringBuider.let {
+            it.append("This is a transformation function.")
+            it.append("It takes a StringBuilder instance and returns the number of characters in the generated String")
+            it.length
+        }
+        assertThat(numberOfCharacters).isEqualTo(128)
+    }
+
+    @Test
+    fun shouldHandleNullabilityWhenLetFunctionUsed() {
+
+        val message: String? = "hello there!"
+        val charactersInMessage = message?.let {
+            "At this point is safe to reference the variable. Let's print the message: $it"
+        } ?: "default value"
+
+        assertThat(charactersInMessage).isEqualTo("At this point is safe to reference the variable. Let's print the message: hello there!")
+
+        val aNullMessage = null
+        val thisIsNull = aNullMessage?.let {
+            "At this point it would be safe to reference the variable. But it will not really happen because it is null. Let's reference: $it"
+        } ?: "default value"
+
+        assertThat(thisIsNull).isEqualTo("default value")
+    }
+
+    @Test
+    fun shouldInitializeObjectWhenUsingApply() {
+        val aStudent = Student().apply {
+            studentId = "1234567"
+            name = "Mary"
+            surname = "Smith"
+        }
+        assertThat(aStudent.name).isEqualTo("Mary")
+    }
+
+    @Test
+    fun shouldAllowBuilderStyleObjectDesignWhenApplyUsedInClassMethods() {
+        val teacher = Teacher()
+            .setId(1000)
+            .setName("Martha")
+            .setSurname("Spector")
+
+        assertThat(teacher.surname).isEqualTo("Spector")
+    }
+
+    @Test
+    fun shouldAllowSideEffectWhenUsingAlso() {
+        val restClient = RestClient("http://www.someurl.com")
+
+        val logger = Logger()
+
+        val headers = restClient
+            .getResponse()
+            .also { logger.info(it.toString()) }
+            .headers
+
+        assertThat(logger.wasCalled()).isTrue()
+        assertThat(headers.headerInfo).isEqualTo("some header info")
+    }
+
+    @Test
+    fun shouldInitializeFieldWhenAlsoUsed() {
+        val aStudent = Student().also { it.name = "John"}
+        assertThat(aStudent.name).isEqualTo("John")
+    }
+
+    @Test
+    fun shouldLogicallyGroupObjectCallsWhenUsingWith() {
+        val bankAccount = BankAccount(1000)
+        with (bankAccount) {
+            checkAuthorization("someone")
+            addPayee("some payee")
+            makePayment("payment information")
+        }
+    }
+
+    @Test
+    fun shouldConvertObjectWhenRunUsed() {
+        val stringBuider = StringBuilder()
+        val numberOfCharacters = stringBuider.run {
+            append("This is a transformation function.")
+            append("It takes a StringBuilder instance and returns the number of characters in the generated String")
+            length
+        }
+        assertThat(numberOfCharacters).isEqualTo(128)
+    }
+
+    @Test
+    fun shouldHandleNullabilityWhenRunIsUsed() {
+        val message: String? = "hello there!"
+        val charactersInMessage = message?.run {
+            "At this point is safe to reference the variable. Let's print the message: $this"
+        } ?: "default value"
+        assertThat(charactersInMessage).isEqualTo("At this point is safe to reference the variable. Let's print the message: hello there!")
+    }
+
+}