Reflection with Swift - Get Functions Name of a Class

Reflection with Swift - Get functions name of a class

Reflection in Swift is very limited compared to the hackeries available in Objective-C. Having said that, the Objective-C runtime functions are still available in Swift. You can sneak your class into the Objective-C world by making it inherit from NSObject:

class MyClass: NSObject {
    func f1() {}
    func f2() {}
    func f3() {}
}

let myClass = MyClass.self

var methodCount: UInt32 = 0
let methodList = class_copyMethodList(myClass, &methodCount)

for i in 0..<Int(methodCount) {
    let selName = sel_getName(method_getName(methodList[i]))
    let methodName = String(CString: selName, encoding: NSUTF8StringEncoding)!
    print(methodName)
}

This will give you 4 methods: f1 ... f3 and init.

(Reflection) Calling A Method With Parameters By Function Name In Swift

First of all, as you noted Swift doesn't have full reflection capabilities and rely on the coexisting ObjC to provide these features.

So even if you can write pure Swift code, you will need Solution to be a subclass of NSObject (or implement NSObjectProtocol).

Playground sample:

class Solution: NSObject {

    @objc func functionName(greeting: String, name: String) {
        print(greeting, name)
    }

}

let solutionInstance = Solution() as NSObject
let selector = #selector(Solution.functionName)
if solutionInstance.responds(to: selector) {
    solutionInstance.perform(selector, with: "Hello", with: "solution")
}

There are other points of concern here:

• Swift's perform is limited to 2 parameters
• you need to have the exact signature of the method (#selector here)

If you can stick an array in the first parameters, and alway have the same signature then you're done.
But if you really need to go further you have no choice than to go with ObjC, which doesn't work in Playground.

You could create a Driver.m file of the like:

#import <Foundation/Foundation.h>
#import <objc/runtime.h>

id call (NSObject *callOn, NSString *callMethod, NSArray <NSObject *>*callParameters)
{
    void *result = NULL;
    unsigned int index, count;

    Method *methods = class_copyMethodList(callOn.class, &count);
    for (index = 0; index < count; ++index)
    {
        Method method = methods[index];

        struct objc_method_description *description = method_getDescription(method);
        NSString *name = [NSString stringWithUTF8String:sel_getName(description->name)];
        if ([name isEqualToString:callMethod])
        {
            NSMethodSignature *signature = [NSMethodSignature signatureWithObjCTypes:description->types];
            NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];

            NSObject *parameters[callParameters.count];
            for (int p = 0; p < callParameters.count; ++p) {
                parameters[p] = [callParameters objectAtIndex:p];
                [invocation setArgument:¶meters[p] atIndex:p + 2]; // 0 is self 1 is SEL
            }
            [invocation setTarget:callOn];
            [invocation setSelector:description->name];
            [invocation invoke];
            [invocation getReturnValue:&result];
            break;
        }
    }
    free(methods);

    return (__bridge id)result;
}

Add it to a bridging-header (for Swift to know about what is in ObjC):

// YourProjectName-Bridging-Header.h
id call (NSObject *callOn, NSString *callMethod, NSArray *callParameters);

And call it with a Solution.swift like this:

import Foundation

class Solution: NSObject {

    override init() {
        super.init()
        // this should go in Driver.swift
        let result = call(self, "functionNameWithGreeting:name:", ["Hello", "solution"])
        print(result as Any)
    }

    @objc
    func functionName(greeting: String, name: String) -> String {
        print(greeting, name)
        return "return"
    }

}

output:

Hello solution
Optional(return)

Edit: compilation

To compile both ObjC and Swift on the command line you can first compile ObjC to an object file:

$ cc -O -c YouObjCFile.m

Then compile your Swift project with the bridging header and the object file:

$ swiftc -import-objc-header ../Your-Bridging-Header.h YouObjCFile.o AllYourSwiftFiles.swift -o program

working sample

Swift 5 reflection get list of class properties and call them

From the docs:

Describes the instance methods implemented by a class.

constMethod1 and constMethod2 are computed class properties, which translates to class methods in Objective-C. So they won't be returned by class_copyMethodList. But fear not, the docs also say:

To get the class methods of a class, use class_copyMethodList(object_getClass(cls), &count).

So you can do:

let methodList = class_copyMethodList(object_getClass(MyClass.self), &methodCount)

To call it, you can use perform:

if crtMethodStr.hasPrefix("const") {
    let result = MyClass.perform(method_getName(unwrapped!))!.takeUnretainedValue()
    print(result)
}

Get a Swift class's property name as a String

If you are ok with making your properties @objc you can get the property name like so:

class Person {
    @objc var firstName: String
    var lastName: String
    var downloading: Bool

    func excludePropertiesFromCloud() -> [String] {
        return [#keyPath(firstName)]
    }
}

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