Merge pull request #903 from zeesh49/KTLN-654-Railway-Orient-Programming-in-Kotlin

Code added for KTLN-654: Railway Oriented Programming

Author: davidmartinezbarua

kotlin-patterns/src/main/kotlin/com/baeldung/railwayorientedprogramming/ROP.kt

@@ -0,0 +1,29 @@
+package com.baeldung.railwayorientedprogramming
+
+data class Customer(val name: String, val emailAddress: String)
+
+object ROP {
+    fun createAndSave(args: Array<String>): Result<String> {
+        return validateName(args.toList()) then ::validateEmail then ::createCustomerDAO then ::save
+    }
+
+    fun validateName(inp: List<String>): Result<List<String>> {
+        if(inp.get(0).length < 10) {
+            return Failure("Name validation failed. Name must be greater than 10 characters.")
+        }else{
+            return Success(inp)
+        }
+    }
+
+    fun validateEmail(inp: List<String>): Result<List<String>> {
+        if(inp.get(1).contains("@")) {
+            return Success(inp)
+        }else{
+            return Failure("Email validation failed. Email must contain '@' symbol.")
+        }
+    }
+
+    fun createCustomerDAO(inp: List<String>): Result<Customer> = Success(Customer(inp.get(0), inp.get(1)))
+
+    fun save(customer: Customer): Result<String> { return Success("Customer successfully saved: " + customer) }
+}

kotlin-patterns/src/main/kotlin/com/baeldung/railwayorientedprogramming/Result.kt

@@ -0,0 +1,13 @@
+package com.baeldung.railwayorientedprogramming
+
+sealed class Result<T>
+data class Success<T>(val value: T): Result<T>()
+data class Failure<T>(val errorMessage: String): Result<T>()
+infix fun <T,U> Result<T>.then(f: (T) -> Result<U>) =
+    when (this) {
+        is Success -> f(this.value)
+        is Failure -> Failure(this.errorMessage)
+    }
+
+infix fun <T> Result<T>.otherwise(f: (String) -> Unit) =
+    if (this is Failure) f(this.errorMessage) else Unit

kotlin-patterns/src/test/java/com/baeldung/railwayorientedprogramming/ROPUnitTest.kt

@@ -0,0 +1,38 @@
+package com.baeldung.railwayorientedprogramming
+
+import org.junit.jupiter.api.Assertions.assertInstanceOf
+import org.junit.jupiter.api.Test
+
+class ROPUnitTest {
+    @Test
+    fun `create and save customer successfully`() {;
+        val customer = Customer("Zeeshan Arif Saeed"
+            , "[email protected]")
+        val res = ROP.createAndSave(arrayOf("Zeeshan Arif Saeed"
+            , "[email protected]"))
+        assertInstanceOf(res::class.java,
+            Success("Customer successfully saved: " + customer))
+    }
+
+    @Test
+    fun `create and save customer name validatation failure`() {;
+        val customer = Customer("Zeeshan"
+            , "[email protected]")
+        val res = ROP.createAndSave(arrayOf("Zeeshan"
+            , "[email protected]"))
+        assertInstanceOf(res::class.java,
+            Failure<String>("Name validation failed. Name must be greater than 10 characters.")
+        )
+    }
+
+    @Test
+    fun `create and save customer email validatation failure`() {;
+        val customer = Customer("Zeeshan Arif Saeed"
+            , "[email protected]")
+        val res = ROP.createAndSave(arrayOf("Zeeshan"
+            , "[email protected]"))
+        assertInstanceOf(res::class.java,
+            Failure<String>("Email validation failed. Email must contain '@' symbol.")
+        )
+    }
+}