Enough examples for now

src/main/kotlin/t20_Apply/bad.kt

@@ -0,0 +1,11 @@
+package t20_Apply.bad
+
+import java.awt.Color
+import javax.swing.JLabel
+
+fun createLabel(): JLabel {
+    val label = JLabel("Foo")
+    label.foreground = Color.RED
+    label.background = Color.BLUE
+    return label
+}

src/main/kotlin/t20_Apply/good.kt

@@ -0,0 +1,9 @@
+package t20_Apply.good
+
+import java.awt.Color
+import javax.swing.JLabel
+
+fun createLabel() = JLabel("Foo").apply {
+    foreground = Color.RED
+    background = Color.BLUE
+}

src/main/kotlin/t21_FilterIsInstance/bad.kt

@@ -0,0 +1,4 @@
+package t21_FilterIsInstance.bad
+
+fun findAllStrings(objects: List<Any>) =
+    objects.filter { it is String }

src/main/kotlin/t21_FilterIsInstance/good.kt

@@ -0,0 +1,4 @@
+package t21_FilterIsInstance.good
+
+fun findAllStrings(objects: List<Any>) =
+    objects.filterIsInstance<String>()

src/main/kotlin/t22_MapNotNull/bad.kt

@@ -0,0 +1,9 @@
+package t22_MapNotNull.bad
+
+data class Result(val data: Any?,
+                  val errorMessage: String?)
+
+fun listAllErrorMessages(errors: List<Result>): List<String> =
+    errors.map { it.errorMessage }.filterNotNull()
+
+

src/main/kotlin/t22_MapNotNull/good.kt

@@ -0,0 +1,7 @@
+package t22_MapNotNull.good
+
+data class Result(val data: Any?,
+                  val errorMessage: String?)
+
+fun listAllErrorMessages(errors: List<Result>): List<String> =
+    errors.mapNotNull { it.errorMessage }

src/main/kotlin/t23_CompareBy/bad.kt

@@ -0,0 +1,12 @@
+package t23_CompareBy.bad
+
+class Person(val name: String, val age: Int)
+
+fun sortPersons(persons: List<Person>) =
+    persons.sortedWith(Comparator<Person> { person1, person2 ->
+        val rc = person1.name.compareTo(person2.name)
+        if (rc != 0)
+            rc
+        else
+            person1.age - person2.age
+    })

src/main/kotlin/t23_CompareBy/good.kt

@@ -0,0 +1,6 @@
+package t23_CompareBy.good
+
+class Person(val name: String, val age: Int)
+
+fun sortPersons(persons: List<Person>) =
+    persons.sortedWith(compareBy(Person::name, Person::age))

src/main/kotlin/t24_Zip/bad.kt

@@ -0,0 +1,7 @@
+package t24_Zip.bad
+
+fun calculateRequestDurations(requestTimestamps: LongArray,
+                              responseTimestamps: LongArray) =
+    requestTimestamps.mapIndexed { index, req ->
+        responseTimestamps[index] - req
+    }

src/main/kotlin/t24_Zip/good.kt

@@ -0,0 +1,5 @@
+package t24_Zip.good
+
+fun calculateRequestDurations(requestTimestamps: LongArray,
+                              responseTimestamps: LongArray) =
+     (requestTimestamps zip responseTimestamps).map { (req, res) -> res - req }

src/main/kotlin/t25_GroupBy/bad.kt

@@ -0,0 +1,11 @@
+package t25_GroupBy.bad
+
+class Request(val url: String, val remoteIP: String, val timestamp: Long)
+
+fun analyzeRequests(log: List<Request>) {
+    val map = mutableMapOf<String, MutableList<Request>>()
+    for (request in log) {
+        map.getOrPut(request.url) { mutableListOf() }
+                .add(request)
+    }
+}

src/main/kotlin/t25_GroupBy/good.kt

@@ -0,0 +1,7 @@
+package t25_GroupBy.good
+
+class Request(val url: String, val remoteIP: String, val timestamp: Long)
+
+fun analyzeRequests(log: List<Request>) {
+    val map = log.groupBy(Request::url)
+}

src/main/kotlin/t26_SubstringBeforeLast/bad.kt

@@ -0,0 +1,14 @@
+package t26_SubstringBeforeLast.bad
+
+data class PathComponents(val directory: String,
+                          val pathName: String)
+
+val pattern = Regex("(.+)/([^/]*)")
+
+fun splitPath(path: String): PathComponents {
+    val match = pattern.matchEntire(path)
+            ?: return PathComponents("", path)
+
+    return PathComponents(match.groupValues[1],
+            match.groupValues[2])
+}

src/main/kotlin/t26_SubstringBeforeLast/good.kt

@@ -0,0 +1,9 @@
+package t26_SubstringBeforeLast.good
+
+data class PathComponents(val directory: String,
+                          val pathName: String)
+
+fun splitPath(path: String): PathComponents {
+    return PathComponents(path.substringBeforeLast('/', ""),
+            path.substringAfterLast('/'))
+}