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swiftのオプショナル型がちょっと腹に落ちた

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概要

Optional型がちょっと腹に落ちたので、その辺のまとめあたり

http://qiita.com/cotrpepe/items/e30c7442733b93adf46a
ここによると

Optional型 : nilが入るのを許す
非Optional型 : nilが入るのを許さない

ふむ

宣言方法

var a: Int? // Optional型
var b: Int  // 非Optional型

var c: String? // Optional型
var d: String  // 非Optional型

オプショナル型は、基本Stringの後にびっくりマークがつきます
びっくりを省略すると強制的に非Optional型
では、早速使ってみよう

例えば

var d: String

if d != nil {
}

上記はif文でエラーです。だって、変数dは非オプショナルなので
nilが入るわけない。

他にもこれってパターンがあるんだろうけど、それは今後追記していく

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