Immutable value as inout argument

问题:

I would like to have a pointer as a parameter of a class. But when I am trying to code the init, I am having this error: Cannot pass immutable value of type 'AnyObject?' as inout argument

class MyClass {     var valuePointer: UnsafeMutablePointer<AnyObject?>      init(value: inout AnyObject?) {         self.valuePointer = &value     } } 

I would like to create some instance of MyClass which can all refer to the same "value". Then, when I am editing this value in this class, it would change everywhere else.

This is the first time I'm working with pointer in Swift. I guess I am doing it wrong...

回答1:

For those who has the cannot pass immutable value as inout argument error. Check that your argument is not optional first. Inout type doesn't seems to like optional values.

回答2:

You could send the pointer when initializing the object:

class MyClass {     var valuePointer: UnsafeMutablePointer<AnyObject?>      init(value: inout UnsafeMutablePointer<AnyObject?>) {         self.valuePointer = value     } } 

Just add the pointer reference when initializing MyClass:

let obj = MyClass(value: &obj2) 

回答3:

For me, I had a class variable defined like this:

// file MyClass.swift  class MyClass{      var myVariable:SomeClass!      var otherVariable:OtherClass!      ...      func someFunction(){         otherVariable.delegateFunction(parameter: &myVariable) // error     } }  // file OtherClass.swift class OtherClass{     func delegateFunction(parameter: inout myVariable){         // modify myVariable's data members      } } 

There error that was invoked was:

Cannot pass immutable value as inout argument: 'self' is immutable 

I then changed my variable declaration in MyClass.swift to no longer have ! and instead initially point to some dummy instance of a class.

var myVariable:SomeClass = SomeClass()  

My code was then able to compile and run as intended. So... somehow having the ! on a class variable prevents you from passing that variable as an inout variable. I do not understand why.

回答4:

For someone faced the same issue with me:

Cannot pass immutable value as inout argument: implicit conversion from '' to '' requires a temporary

The code as below:

protocol FooProtocol {     var a: String{get set} }  class Foo: FooProtocol {     var a: String     init(a: String) {         self.a = a     } }  func update(foo: inout FooProtocol) {     foo.a = "new string" }  var f = Foo(a: "First String") update(foo: &f)//Error: Cannot pass immutable value as inout argument: implicit conversion from 'Foo' to 'FooProtocol' requires a temporary 

Change from var f = Foo(a: "First String") to var f: FooProtocol = Foo(a: "First String") fixed the Error.

文章来源: Immutable value as inout argument