swift optionals - 1
学习是个循序渐进的过程,万事开头难. Swift说起来简单易上手,但有一些知识要反复琢磨,多加练习,才会深入理解。
Need to practise a lot and test what is Optiontal Type and how to use it very well
Optional 介绍:
An optional value either contains a value or contains nil (no value) to indicate that a value is missing. Write a question mark (?) after the type of a value to mark the value as optional.
If a var or constant could be a nil, the var must be declared as optional
Optional is an enumeration
Optional 例子:
1. pNumber is a string constant
2. when cast it to a Int, it might be a Int or nil since some strings can not be casted, liked "good"
3. Optional binding statement is if let a = b {}
If you are sure the optional does contain a value, it can be accessed by pNumber! (Implicitly optional)
Sample code:
let pNumber = "123"
//let converterNumber = Int(possibleNumber!)
if let actualNumber = Int(pNumber) { //casting and force it to a constant. A constan
print("\'\(pNumber)\' has an integer valuel of \(actualNumber)")
} else {
print("\'\(pNumber)\' could not be converted to an integer")
}