Swift

1. Structs vs. Classes

   Try to use structs over classes when possible. They are safer in a multi-thread environment, faster, they have a default init method and many other benefits. But understand the difference and keep in mind that structs are a value type while classes are a reference type, meaning that each instance of a struct has its own unique copy of it, while each instance of a class has a reference to one single copy of the data.

2. Subscripts

    extension String {
        subscript(i: Int) -> String {
            return String(self[index(startIndex, offsetBy: i)])
        }
    }
   

   Usage:

    let str = "Hello, Playground!" 
    print("Letter at index 7 is \(str[7])")
   

   Output:

    Letter at index 7 is P
   

References

1. Medium
2. hackingwithswift