Swift Protocol Error: 'Weak' Cannot Be Applied to Non-Class Type

Swift protocol error: 'weak' cannot be applied to non-class type

Swift >= 4:

protocol A : AnyObject { ... {

Swift < 4:

protocol A : class { ... }

defines a "class-only protocol": Only class types (and not structures or enumerations) can adopt this protocol.

Weak references are only defined for reference types. Classes
are reference types, structures and enumerations are value types.
(Closures are reference types as well, but closures cannot adopt
a protocol, so they are irrelevant in this context.)

Therefore, if the object conforming to the protocol needs to be stored in a weak property then the protocol must be a class-only protocol.

Here is another example which requires a class-only protocol:

protocol A { 
    var name : String { get set }
}

func foo(a : A) {
    a.name = "bar" // error: cannot assign to property: 'a' is a 'let' constant
}

This does not compile because for instances of structures and enumerations, a.name = "bar" is a mutation of a. If you define
the protocol as

protocol A : class { 
    var name : String { get set }
}

then the compiler knows that a is an instance of a class type to that
a is a reference to the object storage,
and a.name = "bar" modifies the referenced object, but not a.

So generally, you would define a class-only protocol if you need
the types adopting the protocol to be reference types and not value types.

Why can the keyword weak only be applied to class and class-bound protocol types

weak is a qualifier for reference types (as opposed to value types, such as structs and built-in value types).

Reference types let you have multiple references to the same object. The object gets deallocated when the last strong reference stops referencing it (weak references do not count).

Value types, on the other hand, are assigned by copy. Reference counting does not apply, so weak modifier does not make sense with them.

weak' cannot be applied to non-class type ' error type '

Is the button you are using placed in a local framework? if so try to rebuild the framework first, if you are not sure try next steps.

If you say that everybody else can run the project, it seems that your build folder got mess. You can try this steps in order to clean it

1. Remove app from device
2. In Xcode within your project press cmd + alt + shift + K
3. Clean Derived data of the project (Go to window > Projects > Don't press Delete, press the arrow next to the path, remove all files and folders from there)

Now, when you will press start, a new and clean build will be made

Update
you mentioned you use pods to manage your project, do a pod outdated - to check if there are any pods outdated, you are interested in the one with the button mostly, if so do an update on it

Alamofire: 'weak' cannot be applied to non-class type error

Paulw11 is correct. Because I am using static, that's why self does not make any sense. Low level mistake. Problem solved.

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