This is an automated email from the ASF dual-hosted git repository.
joshtynjala pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/royale-docs.git
commit 002c78bf1d981c1aec034c30877723bfe3596564
Author: Josh Tynjala <joshtynj...@apache.org>
AuthorDate: Thu Aug 21 15:14:12 2025 -0700
arrow-functions
---
features/as3.md | 1 +
features/as3/arrow-functions.md | 111 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 112 insertions(+)
diff --git a/features/as3.md b/features/as3.md
index 8069e0c..ae5d711 100644
--- a/features/as3.md
+++ b/features/as3.md
@@ -65,6 +65,7 @@ The Royale compiler extends the ActionScript language with
useful, new features.
The following new ActionScript features are available with the Royale compiler:
* [Abstract Classes](features/as3/abstract-classes)
+* [Arrow Functions](features/as3/arrow-functions)
* [Import Aliases](features/as3/import-aliases)
* [Null Conditional Operator](features/as3/null-conditional-operator)
* [Nullish Coalescing Operator](features/as3/nullish-coalescing-operator)
diff --git a/features/as3/arrow-functions.md b/features/as3/arrow-functions.md
new file mode 100644
index 0000000..c2cbf6b
--- /dev/null
+++ b/features/as3/arrow-functions.md
@@ -0,0 +1,111 @@
+---
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements. See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You 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
+#
+# http://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.
+
+
+layout: docpage
+title: Arrow functions
+description: Arrow function expressions in ActionScript
+permalink: /features/as3/arrow-functions
+---
+
+# Arrow function expressions in ActionScript
+
+-allow-arrow-functions
+
+[Apache Royale](https://royale.apache.org/){:target='_blank'} adds support for
arrow function expressions in [ActionScript](features/as3). An arrow function
provides shorter syntax for declaring local functions, and it inherits the
`this` value from its containing scope.
+
+Arrow functions do not have names. Unlike regular function expressions, arrow
functions omit the `function` keyword, and they have an arrow (in the format
`=>`) between the parameters and the body instead. In certain situations, both
the parentheses around the parameters and the braces around the body may be
omitted.
+
+_Requires Apache Royale 0.9.13 or newer._
+
+## Compiler option
+
+Royale enables arrow functions by default. To disable arrow functions in your
application, use the `-allow-arrow-functions` compiler option.
+
+```sh
+mxmlc -allow-arrow-functions=false MyApp.mxml
+```
+
+## Code examples
+
+A simple, traditional function expression might be defined like this:
+
+```as3
+var func:Function = function(name:String):String
+{
+ return "Hello, " + name;
+}
+```
+
+One may replace it with an arrow function expression with equivalent
+behavior, but shorter syntax:
+
+```as3
+var func:Function = (name:String) => "Hello, " + name;
+```
+
+The arrow function expression above has the following differences in syntax:
+
+- Arrow functions do not start with a `function` keyword. Instead, they
include an arrow (`=>`) symbol between the signature and the body.
+- When the body of an arrow function contains a single expression, the `{}`
braces are considered optional and may be omitted.
+- If the braces are omitted, the result of the single expression in the body
is automatically returned. In fact, one is not allowed to use the `return`
keyword when the braces are omitted.
+- If the braces are omitted, the return type does not need to be declared. The
compiler can automatically infer a return type from the single expression in
the body.
+
+Omitting parts of an arrow function is optional, but some may prefer to
include the braces, the return type, and the `return` keyword.
+
+```as3
+var func:Function = (name:String):String => {
+ return "Hello, " + name;
+}
+```
+
+If an arrow function has a single parameter, the parentheses around that
parameter become optional when the parameter is simply an identifier, with no
declared type and no default value. However, omitting the type of the parameter
will result in a compiler warning, and the type will default to `*`, so it is
not recommended.
+
+```as3
+var func:Function = name => "Hello, " + name;
+// Warning: return value for function has no type declaration.
+```
+
+### Using `this` in arrow functions
+
+When a function object is created within a method, and it needs to access the
value of `this`, using an arrow function expression can lead to simpler code.
+
+```as3
+class MyClass {
+ public function createCallback():Function {
+ return () => this;
+ }
+}
+```
+
+In comparison, using a regular function expression is more verbose because
`this` from the outer scope needs to be saved in a local variable:
+
+```as3
+class MyClass {
+ public function createCallback():Function {
+ var self:MyClass = this;
+ return function():MyClass {
+ return self;
+ }
+ }
+}
+```
+
+Attempting to use `this` directly in the function object would return the
global object instead of an instance of `MyClass`.
+
+## Limitations of arrow functions in Royale
+
+Other ActionScript compilers, such as the one in the [Apache Flex
SDK](https://flex.apache.org/){:target='_blank'}, may not recognize arrow
functions. Attemping to pass ActionScript or MXML source code that contain
arrow functions to another compiler may result in compile-time errors. In other
words, to write 100% portable ActionScript code that works with any compiler,
avoid using arrow functions and any of Royale's other [extensions to the
ActionScript language](features/as3#new-action [...]
