var userName:String?
// println("Hello," + userName ?? "Guest") ×
println("Hello," + (userName ?? "Guest")) ○
// println("Hello," + userName ?? "Guest") ×
println("Hello," + (userName ?? "Guest")) ○
2014-12-21
swift強(qiáng)制讓有默認(rèn)值的參數(shù)使用外部參數(shù)名的原因應(yīng)該是 有默認(rèn)值的參數(shù)同時(shí)是可選的 在有多個(gè)可選參數(shù)的時(shí)候 不加外部參數(shù)名 可能導(dǎo)致開發(fā)者傳入的參數(shù)順序出錯(cuò)
2014-12-16