學(xué)習(xí)是個(gè)循序漸進(jìn)的過程，萬事開頭難. Swift說起來簡單易上手，但有一些知識(shí)要反復(fù)琢磨，多加練習(xí)，才會(huì)深入理解。

Need to practise a lot and test what is Optiontal Type and how to use it very well

Optional 介紹：?

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")

}

轉(zhuǎn)載于:https://www.cnblogs.com/iyoubo/p/4609319.html

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