ExceptionCatcher

Catch Objective-C exceptions in Swift! 🪤

Details

There are many Cocoa APIs that can throw exceptions that cannot be caught in Swift (for instance NSKeyedUnarchiver, NSTask, NSObject#value(forKey:)). This package wraps an Objective-C exception handler to make it possible to catch such exceptions.

The ability to catch exceptions should really be built into Swift. If you agree, duplicate this Feedback Assistant report.

Setup

Add the following to Package.swift:

.package(url: "https://github.com/stateman92/ExceptionCatcher", exact: .init(2, 0, 8))

Or add the package in Xcode.

Usage

import ExceptionCatcher

final class Foo: NSObject {}

do {
    let value = try ExceptionCatcher.rethrow {
        Foo().value(forKey: "nope")
    }
    print("Value: ", value)
} catch {
    print("Error: ", error.localizedDescription)
    // Error: [<ExceptionCatcher.Foo 0x6000034c0030> valueForUndefinedKey:]: this class is not key value coding-compliant for the key nope.

    debugPrint(error)
    /*
    Error Domain=NSUnknownKeyException Code=0 "[valueForUndefinedKey:]: this class is not key value coding-compliant for the key nope." UserInfo={CallStackSymbols=(
    0   CoreFoundation                      0x00007fff361798ab __exceptionPreprocess + 250
    1   libobjc.A.dylib                     0x00007fff6c3ea805 objc_exception_throw + 48
    2   CoreFoundation                      0x00007fff361a230c -[NSException raise] + 9
    3   Foundation                          0x00007fff388f86c4 -[NSObject(NSKeyValueCoding) valueForUndefinedKey:] + 222
    4   Foundation                          0x00007fff3876f8fd -[NSObject(NSKeyValueCoding) valueForKey:] + 317
    …
    */
}

For details see the Example app.

Tests

The library is well-tested with the coverage percentage of 94.4%, which cannot be improved since the missing parts (a single line) should never be reached.