I have a function that is called by javascript with JavascriptCore.
Now inside that function I have to evaluate a javascript again under a certain condition. This should call the same function.
let My_JS_Function: #convention(block) ( String, String, String ) -> ( ) = {
thing_1, thing_2, thing_3
in
let my_Condition = true
if my_Condition {
let c = JSContext()
// compiling error: "Variable used within its own initial value"
Context.setObject(unsafeBitCast(My_JS_Function, AnyObject.self), forKeyedSubscript: "My_JS_Function")
c.evaluateScript("My_JS_Function("value 1","value 2","value 3");")
}
}
Now XCode tells me:
Variable used within its own initial value
Does anybody know wheather there's a way how to solve this problem?
Maybe a way to write the My_JS_Function as a function and not like here as a variable?
I could fix the problem with avoiding having functions as properties.
Therefor I put the functionality in an extra class and used JSExport.
One example for how it can be done with JSExport can be found here.
Related
I'm having an issue with evaluation of one line of code
if i break it down to two lines, it's working , but in one line of code, it's just evaluate in a 'new' to a 'wrong' way.
my main reason for asking this question, is not to solve it, I know I can use parenthesis to solve it, and break it to Two line, but don't want to solve it, I just want to know why its evaluated like this , and if there's a solution for this : some setting to patch , in Order THAT it will work in ONE LINE OF CODE :
Heres the code that working in Two lines
Heres the code that trying to do the same thing, but rise an error as you can see:
full code of both working and not working :
class ClosuresStack {
var dic = Dictionary<String,(()->String)->String >()
subscript(_ str:String)-> (()->String)->String {
get {
return dic[str]!
}
set {
dic[str] = newValue
}
}
}
func createClosuresStak() -> ClosuresStack {
let cs = ClosuresStack()
func takesAClosureReturnA_string(_ closure:()->String) ->String {
return closure() + " Two"
}
cs["C"] = takesAClosureReturnA_string
return cs
}
let c = createClosuresStak()["C"]
let str = c{"One"}
print(str) // print: One Two
let c = createClosuresStak()["C"]{"One"} // error -->
now, I want to somehow understand how to change it that it will work in ONE LINE OF CODE : meaning that the evaluation of 'createClosuresStak()["C"]{"One"}' will create a closure after ["C"] , and then from that point writing the {"One"}
will make it a full evaluate of the line :
let c = createClosuresStak()["C"]{"One"}
making 'c' a String
if that's not possible, I need to know it Too , tnx :)
UPDATE
tnx for the comments , its help me understand the problem more clearly :
1) im understanding that the createClosuresStak()["C"]{"One"}
acutely trying to add the string 'One' as another parameter to the sub script , and there for the error from the compiler was that is cannot subscript (String,()->String} , 'C' as the string inside the [] , and the other parameter {"One"} -> BUT , isn't that some kind of a bug?, been that i'm using [] ,Cleary the compiler need to 'understand' that I want to subscript a String, also by power of inferring that swift has,
2) now I'm still trying to get that syntax to work as it is so I try to change some things, in order to get it to work :
so I created a function that take a string, and return a dictionary of type : Dictionary<String,()->String>, and then trying so subscript it
and the compiler don't rise an error that way :
func closuresDictionary(_ s:String) -> Dictionary<String,()->String> {
var dic = Dictionary<String,()->String>()
func foo()->String {
return s + " Two"
}
dic["C"] = foo
return dic
}
let c = closuresDictionary("One")["C"]{ "SomeString" }
c is now a closure of type ()->String which does noting with string that I put inside, so the syntax works, but the outcome is not doing anything.
when im changing the return type of the dictionary to a different closure : (String)->String instead of ()->String , im getting the same old error, that I'm trying to subscript a (String,(String)->String)
and I need a function that will take the string inside the {} , and create something from it meaning that I need to subscript to return a closure of (String)->String
its seems like there's no way to do that
im adding two more pictures of my last trying in order to get this line of code in current syntax to work
the wanted syntax working but the outcome is not an outcome not doing any thing with the string inside the {}:
same error, by changing the function to (String)->String
Your example:
let c = createClosuresStak()["C"]{"One"}
is using trailing closure syntax.
Trailing closure syntax works by including the trailing closure as an additional parameter to a function call. Subscripting an array is really a function call under the hood (to a function called subscript), and Swift is trying to pass that closure as a second parameter to the subscripting call, which is what the error is explaining:
Cannot subscript a value of type 'ClosuresStack' with an argument of type '(String, () -> String)'.
In other words, you can't pass both "C" and the closure {"One"} to the subscripting function.
There are at least 3 ways to fix this and still put it on one line:
Option 1: Use an explicit call to pass the closure instead of using trailing closure syntax
Wrap the closure in () to make the call explicit:
let c1 = createClosuresStak()["C"]({"One"})
print(c1)
Option 2: Wrap the createClosureStak()["C"] in parentheses
That lets Swift know the subscripting only gets "C" as a parameter and allows trailing closure syntax to work as expected:
let c2 = (createClosuresStak()["C"]){"One"}
print(c2)
Option 3: Add .self to the result before the trailing closure syntax:
That again finishes the subscripting call and avoids the confusion.
let c3 = createClosuresStak()["C"].self {"One"}
print(c3)
Personally, I would choose option one, because trailing closure syntax is unnecessary syntactic sugar that clearly is not working here.
I have a function that returns a completion. The completion has as in parameter a custom class with a dictionary that uses an enum as an identifier.
The problem I am facing is that Xcode does not recognises the type of the variable and does not auto complete when I use it inside of completion block.
My code looks like that
Function
func testFunc (completion:(PrxServiceResponseCallback) ->()){
let responseCallback = PrxServiceResponseCallback()
completion(responseCallback)
}
Class
class PrxServiceResponseCallback:NSObject{
var success = false
var resultCode:Int32 = 0
var response:[PrxResponseAttributes:Any] = [PrxResponseAttributes:Any]()
}
enum PrxResponseAttributes{
case sourceProtocolInfoArray
case sinkProtocolInfoArray
case connectionIDsArray
case connectionInfo
}
Calling the function
testFunc { (testResonse) in
testResonse.response[.]//Not Auto completing
}
The whole idea of making a dictionary with an enum as identifier was to make easier which attributes the dictionary returns but, If I can't auto complete, the idea is more pointless.
Any ideas?
Xcode doesn't give you autocomplete doesn't mean that your code doesn't compile. It just means that Xcode is too stupid to figure things out. I have encountered such situations many times before. It seems to always happen inside closures.
You can just ignore the fact that no autocomplete shows up and type the case name yourself:
testResonse.response[.sourceProtocolInfoArray]
It will compile.
You can also consider creating a struct instead of storing the values in a dictionary. Here's a sample struct (I guessed the types):
struct Response {
let sourceProtocolInfo: [String]
let sinkProtocolInfo: [String]
let connectionIDs: [Int]
let connectionInfo: String
}
If you use var response:[UIColor:Any] = [UIColor:Any]()
it is still not giving auto complete so it is not your issue and you can not do much on it .
If you need auto complete then use PrxResponseAttributes with . (dot)
you can do it like
testResonse.response[PrxResponseAttributes.sourceProtocolInfoArray]
EDIT
Note: It is only happening with implemented closure if you add one property in your PrxServiceResponseCallback class like
var anyValue:Any? {
return response[.connectionInfo] // it is showing completion
}
In order to do logging nicely, I want to know how to convert argument to argument name string In Swift.
I already know Logging Method signature using swift.
I want to know how to log function argument as it is , following its value?
PS: I want to create a Util method helping logging.
func printMore(objName: Any){
print("objName: \(objName)")
}
the print("objName:..., I want the 'objName' injected automatically.
Suck as conditions:
let foo = "Sark"
print("foo: \(foo)")
PPS: It is about Swift runtime. After I alloc some memory, I create some objects, how to get them through runtime instead of hard coding.
Hm, if you called next method inside your function, it shows method declaration with all parameters:
func testFunction(param1: String, param2: String) {
print(#function)
}
testFunction(param1:param2:)
Write C .
U have to release it youself
object.description
I am new to Swift and am confused with this type of syntax. I know when you add () to the end of something you initialize it. I am still confused what this means though! I am adding code below.
Please help clarify what parenthesis at the end of this means! Thank you!
Also what does it mean to have all that code after the equal sign in this case? ( I know how to create a variable and add a String,Int or something like that to it).
I am just confused a bit wth this code.
Thanks for being understanding to a beginner!
var viewController: ViewController = {
return self.instantiateViewControllerWithIdentifier("Play") as ViewController
}()
EDIT 1 -
var statusBarStyle: UIStatusBarStyle = .Default {
didSet{
setNeedsStatusBarAppearanceUpdate()
}
}
{} declares a closure, which is anonymous function. Everything between { and } is a function body. Since closure defined in provided code does not have arguments it can be executed as regular function by (). { .. }() is just defining and immediately executing of anonymous function.
In a body of a function there is a call of instantiateViewControllerWithIdentifier("Play") which returns AnyObject. As viewController variable (var) expected to ba a type of ViewController, we cast AnyObject result of instantiateViewControllerWithIdentifier as ViewController
As for statusBarStyle, UIStatusBarStyle is an enum. .Default is one of enum's cases. It can be written alternatively as var statusBarStyle = UIStatusBarStyle.Default. The code that goes in the { ... } is a way to declare getter and setter behavior. In this particular case there is only one behavior didSet defined, which means as soon as value of UIStatusBarStyle updated (which is possible, as it is var), call function setNeedsStatusBarAppearanceUpdate. There are other getters & setters keywords that you may read about in Swift Book — https://itunes.apple.com/us/book/swift-programming-language/id881256329 such as get, set, willSet.
As Nikita said its instantly calling the anonymous function you declared. This is really useful as it allows you to add logic when initialising a var or let.
Since the function takes no arguments, it makes it harder to see at first that it actually is a function. An example with an argument makes this concept a lot clearer.
let oneMore: Int = { (num: Int) in num + 1 }(5) //oneMore = 6
We are creating a function that takes one Int argument num and implicitly returns an Int (the compiler knows this because of the type annotation on oneMore. By following the closure with (5) we are calling the anonymous function with the value of 5.
Hopefully this example makes it more clear what happening. Note for an anonymous function in the context we would never need to provide argument since it will only ever be called once with the arguments following it, so we can just include the argument within the function body.
let oneMore: Int = { 5 + 1 }()
In the second example the braces are allowing you to include property observers to the variable. an example of a property observer is didSet which is called each time after you assign a value to the variable. more info can be found in apples docs here.
I'm trying to write a general argmin function in Swift. Here is my code:
func argmin<X, Y:Comparable, R:SequenceType, where X== R.Generator.Element>
(f:(X)->Y, domain:R)->X{
var gen = domain.generate()
var best = gen.next()!
var minval = f(best)
while let this = gen.next() {
let value = f(this)
if value < minval {
best = this
minval = value
}
}
return best
}
I get the error message "Expected identifier to name generic parameter" when I try to compile this definition. I have no idea what this means. It sounds like an error one would get on calling the function, not defining it, but even then, I wouldn't understand it.
I'm just starting to learn Swift. Can you explain this message? (BTW, I know this function will blow up if called with an empty sequence. I'm not worrying about that yet.)
You have to remove this comma:
func argmin<X, Y:Comparable, R:SequenceType, where X== R.Generator.Element>
^
Placed that, it tells the compiler there's another generic parameter. The error message just says that - maybe in a cryptic way, but once you know, it's clearer what it means