SwiftScripting

Utilities and samples to aid in using Swift with the Scripting Bridge

Generating Swift API for a Target Application

The scripting approach leveraged here is a Swift layer on top of the Scripting Bridge. Xcode ships with a pair of utilities, sdef and sdp, to aid Objective-C programmers in using the Scripting Bridge.

The sdef tool is used to extract the scripting definition from an application. It emits the scripting definition to standard output in XML format. The sdp tool can be used to convert the XML emitted by sdef to an Objective-C header file. This header file defines the scripting interface for a target application exposed to Objective-C by the Scripting Bridge.

When scripting applications using Swift, it is possible to leverage the same Objective-C headers emitted by sdp. However, due to the dynamically generated classes involved in realizing the Scripting Bridge interface, this approach can be cumbersome and forces the use of AnyObject types even in areas when more specific types are known to exist.

The approach here is to generate a set of Swift protocols based on the Objective-C header emitted by sdp. In most cases, the generated file can be used without modification. There are some corner cases where manual editing is required to correct issues or workaround bugs in the Swift compiler.

The basic recipe for generating the Swift protocols and enums for a fictitious application called App.app is as follows

1. sdef /Applications/App.app > App.sdef
2. sdp -fh --basename App App.sdef
3. sbhc.py App.h
4. sbsc.py App.sdef

Step 1 will create the App.sdef file in the current directory. Step 2 will create a file App.h, also in the current directory. Step 3 will create App.swift in the current directory. This is the primary file describing the scripting interface. The final step will create the file AppScripting.swift which contains an enum with values appropriate for class creation.

Note that the sbhc.py script leverages the Python bindings for libclang. You must install these bindings before running the script. (pip install 'clang<=16' for macOS 14 Sonoma). You'll also need to install the Xcode command line tools (xcode-select --install.)

See https://majestysoftware.wordpress.com/2015/03/31/swift-scripting-part-1/ for part one of a four-part series that gives a bit of explanation related to SwiftScripting.