Kotlin-ified Coat.

Author: nedtwigg

durian-swt/src/main/java/com/diffplug/common/swt/Coat.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2020 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.common.swt
+
+import com.diffplug.common.swt.Coat.Returning
+import org.eclipse.swt.widgets.Composite
+
+/**
+ * A function that can be "put on" a blank [Composite].
+ *
+ *
+ * An SWT Composite is a blank canvas.  As such, it's common to write functions
+ * that look like `void initializeCmp(Composite cmp)`. In order to make higher-order
+ * functionality, such as a utility for stacking `Composite`s, you need a way to pass
+ * these kinds of functions as arguments. That's what `Coat` does.
+ */
+fun interface Coat {
+    /**
+     * Populates the given composite.
+     * Caller promises that the composite has no layout and contains no children.
+     */
+    fun putOn(cmp: Composite)
+
+    /** A Coat which returns a handle to the content it created.  */
+    fun interface Returning<T> {
+        /**
+         * Populates the given composite, and returns a handle for communicating with the created GUI.
+         * Caller promises that the composite has no layout, and contains no children.
+         */
+        fun putOn(cmp: Composite): T
+
+        companion object {
+            /** Converts a non-returning Coat to a Coat.Returning.  */
+            fun <T> fromNonReturning(coat: Coat, returnValue: T): Returning<T> {
+                return Returning { cmp: Composite ->
+                    coat.putOn(cmp)
+                    returnValue
+                }
+            }
+        }
+    }
+
+    companion object {
+        /** A Coat which does nothing.  */
+		@JvmStatic
+		fun empty(): Coat {
+            return EMPTY
+        }
+
+        val EMPTY = Coat { cmp: Composite -> }
+    }
+}