Swift blocks not working
block, javascriptcore, swift
Solution
It has something to do with how Swift implement closure. You need to use `@convention(block)` to annotate that the closure is ObjC block. Use `unsafeBitCast` to force cast it
var block : @convention(block) (NSString!) -> Void = {
(string : NSString!) -> Void in
println("test")
}
ctx.setObject(unsafeBitCast(block, AnyObject.self), forKeyedSubscript: "test")
from REPL
swift
Welcome to Swift! Type :help for assistance.
1> import Foundation
2> var block : @convention(block)(NSString!) -> Void = {(string : NSString!) -> Void in println("test")}
block: @convention(block)(NSString!) -> Void =
3> var obj: AnyObject = reinterpretCast(block) as AnyObject
obj: __NSMallocBlock__ = {} // familiar block type
Problem
I've been trying to figure out how to use JavaScriptCore in swift. I'm running into problems however when I have to deal with blocks as arguments, seems like the block is run immediately and the arguments gets the return value of the block. What am I doing wrong? Working Objective C code: ``` JSContext* context = [[JSContext alloc] initWithVirtualMachine:[[JSVirtualMachine alloc] init]]; context[@"test"] = ^(NSString *string) { //code }; ``` What I've tried: 1: ``` var ctx = JSContext(virtualMachine:JSVirtualMachine()) var ctx["test"] = {(string:NSString)->() in /*code*/ } //Gives me "'JSContext' does not have a member named 'subscript'" ``` 2: ``` var ctx = JSContext(virtualMachine:JSVirtualMachine()) let n: (string: String)->() = {string in /*code*/} ctx.setObject(n, forKeyedSubscript:"test") //Gives me "Type '(x: String) -> () does not conform to protocol 'AnyObject'" ``` 3: ``` var ctx = JSContext(virtualMachine:JSVirtualMachine()) let n: (string: String)->() = {string in /*code*/} ctx.setObject(n as AnyObject, forKeyedSubscript:"test") //Gives me "Cannot downcast from '(string: String) -> () to non-@objc protocol type 'AnyObject'" ``` Am I missing something here, or is this just a bug in Swift? Edit: I've now also tried suggestions from Cast closures/blocks ``` class Block<T> { let f : T init (_ f: T) { self.f = f } } ``` and then ``` ctx.setObject(Block<()->Void> { /*code*/ }, forKeyedSubscript: "test") ``` This solution lets me compile but I get a runtime error: ``` Thread 1: EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=0x0) ```