Cannot assign to property: 'self' is immutable

struct Test{
    var param1 = false
    
    func method1() {
        param1 = true
    }
}

param1 = true will throw the exception Cannot assign to property: 'self' is immutable

The reason is that struct is saved in stack memory, so its parameters cannot be modified.
But we can change it through mutating:

struct Test{
    var param1 = false
    
    mutating func method1() {
        param1 = true
    }
}

Refer to stack overflow