[swift-users] Referencing Swift Functions from the Objective-C Runtime

[Jeff Kelley]

Still trying on this (copied the code directly, Foo is actually XCTestCase):

typealias TestMethod = @convention(c) (XCTestCase) throws -> Void

This seagulls the compiler with “error: '(XCTestCase) throws -> Void' is not representable in Objective-C, so it cannot be used with '@convention(c)’”. I’m trying to use it here:

let testMethod: IMP = method_getImplementation(method)

let test: TestMethod = unsafeBitCast(testMethod,
                                     to: TestMethod.self)

testMethods.append((methodName as String, test))

If I try to put the type directly in the call to unsafeBitCast(), the compiler gives me an error:

Attribute can only be applied to types, not declarations

Thanks for your suggestions! I hadn’t seen @convention() before.


Jeff Kelley

SlaunchaMan at gmail.com | @SlaunchaMan <https://twitter.com/SlaunchaMan> | jeffkelley.org <http://jeffkelley.org/>
> On Nov 21, 2016, at 12:08 AM, Jacob Bandes-Storch <jtbandes at gmail.com> wrote:
> 
> For a function such as bar() above, the type you want to cast the IMP to would probably be "@convention(c) (Foo, Selector) -> ()".
> 
> On Sun, Nov 20, 2016 at 9:05 PM, Jeff Kelley <slaunchaman at gmail.com <mailto:slaunchaman at gmail.com>> wrote:
> Thanks Jacob! I tried using unsafeBitCast, but it fails with the following: “fatal error: can't unsafeBitCast between types of different sizes”. I considered wrapping every call in a closure that calls objc_msgSend(), but alas, that’s not exposed to Swift. I have another approach in mind, so I’ll try that next.
> 
> 
> Jeff Kelley
> 
> SlaunchaMan at gmail.com <mailto:SlaunchaMan at gmail.com> | @SlaunchaMan <https://twitter.com/SlaunchaMan> | jeffkelley.org <http://jeffkelley.org/>
>> On Nov 19, 2016, at 1:58 AM, Jacob Bandes-Storch <jtbandes at gmail.com <mailto:jtbandes at gmail.com>> wrote:
>> 
>> I imagine unsafeBitCast would be the way to go here. But are you assuming that all of the instance methods have type "(Foo) throws -> Void" ? Or do you somehow want to dynamically use the type information?
>> 
>> Jacob
>> 
>> On Fri, Nov 18, 2016 at 10:37 PM, Jeff Kelley via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>> Hello,
>> 
>> 	I’m trying to enumerate the methods of a class in Swift using the Objective-C runtime. Everything is working fine so far, except for the very last step. Suppose I have a Swift class like this:
>> 
>> class Foo: SomeSuperclass {
>>     
>>     @objc func bar() {
>>         print("Hello, World!")
>>     }
>>     
>> }
>> 
>> 	Using the Objective-C runtime methods, I can get the method with class_copyMethodList and then get to the method’s implementation using method_getImplementation. However, what I need to do next is to stick this into a tuple that looks like this:
>> 
>> typealias FooEntry = (fooClass: SomeSuperclass.Type, methods: [(String, (Foo) throws -> Void)])
>> 
>> 	For now, the workaround is to make a static variable that returns all of the entries:
>> 
>>     static var allEntries = {
>>         return [
>>             ("bar", bar),
>>         ]
>>     }
>> 
>> 	Is there any way to go from the raw IMP that I get back from the runtime to the Swift type so I can construct this list dynamically?
>> 
>> 
>> Jeff Kelley
>> 
>> SlaunchaMan at gmail.com <mailto:SlaunchaMan at gmail.com> | @SlaunchaMan <https://twitter.com/SlaunchaMan> | jeffkelley.org <http://jeffkelley.org/>
>> 
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>> 
> 
> 

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