ios swift中双问号的目的是什么
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what's the purpose of double question mark in swift
提问by Wingzero
I have seen such function:
我见过这样的功能：
public func highlightValues(highs: [ChartHighlight]?)
{
// set the indices to highlight
_indicesToHightlight = highs ?? [ChartHighlight]();
// redraw the chart
setNeedsDisplay();
}
What's the purpose of ??here? I searched, but it seems searching ??is hard to find a proper answer.
来??这里的目的是什么？我搜索过，但似乎搜索??很难找到正确的答案。
回答by mustafa
It is called nil coalescing operator. If highsis not nilthan it is unwrapped and the value returned. If it is nil then [ChartHighlight]()returned. It is a way to give a default value when an optional is nil.
它被称为 nil 合并运算符。如果highs不是nil比它打开并返回的值。如果它是零则[ChartHighlight]()返回。这是一种在可选项为 时给出默认值的方法nil。
