检查 [Type:Type?] 类型的字典中是否存在键 [英] Check if key exists in dictionary of type [Type:Type?]
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问题描述
如何检查字典中是否存在键?我的字典属于 [Type:Type?]
类型.
How can I check if a key exists in a dictionary? My dictionary is of type [Type:Type?]
.
我不能简单地检查 dictionary[key] == nil
,因为这可能是由 nil
的值造成的.
I can't simply check dictionary[key] == nil
, as that could result from the value being nil
.
有什么想法吗?
推荐答案
其实你的测试dictionary[key] == nil
可以用来检查如果字典中存在键.它不会产生 true
如果值设置为 nil
:
Actually your test dictionary[key] == nil
can be used to check
if a key exists in a dictionary. It will not yield true
if the value
is set to nil
:
let dict : [String : Int?] = ["a" : 1, "b" : nil]
dict["a"] == nil // false, dict["a"] is .Some(.Some(1))
dict["b"] == nil // false !!, dict["b"] is .Some(.None)
dict["c"] == nil // true, dict["c"] is .None
要区分字典中不存在键"和键的值为零",您可以做一个嵌套的可选赋值:
To distinguish between "key is not present in dict" and "value for key is nil" you can do a nested optional assignment:
if let val = dict["key"] {
if let x = val {
println(x)
} else {
println("value is nil")
}
} else {
println("key is not present in dict")
}
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