如何在小数字段上搜索？

Question

我是 Swift 新手。

struct Money{
   var amount: Decimal = 0
}

var myMoney = Money()
myMoney.amount = 10.019999999999997952

如果我在

myMoney.amount

上搜索值：10.01，它应该返回 true。我只关心小数点后2位。

我尝试使用范围修改器但没有成功。

Answer 1

如果您只想查看十进制值的字符串表示形式是否以“10.01”等字符串开头...

struct Money{
    var amount: Decimal = 0
    func beginsWith(_ str: String) -> Bool {
        return ("\(amount)").hasPrefix(str)
    }
}

然后：

    var myMoney = Money()
    myMoney.amount = 10.019999999999997952
    
    var searchFor: String = "10.01"
    
    if myMoney.beginsWith(searchFor) {
        print("yes, it begins with:", searchFor)
    } else {
        print("no, it doesn't begin with:", searchFor)
    }

    searchFor = "1001"

    if myMoney.beginsWith(searchFor) {
        print("yes, it begins with:", searchFor)
    } else {
        print("no, it doesn't begin with:", searchFor)
    }
    
    searchFor = "10.02"
    
    if myMoney.beginsWith(searchFor) {
        print("yes, it begins with:", searchFor)
    } else {
        print("no, it doesn't begin with:", searchFor)
    }

调试控制台输出：

yes, it begins with: 10.01
no, it doesn't begin with: 1001
no, it doesn't begin with: 10.02

Answer 2

通常在处理

Decimal

类型时，我们可能会考虑对

amount

中存储的值进行四舍五入：

struct Money{
   var amount: Decimal = 0
}

var myMoney = Money()

var value: Decimal = 10.019999999999997952
NSDecimalRound(&myMoney.amount, &value, 2, .down) // or `.plain`

print(myMoney.amount)

或者，如果您经常这样做，您可以定义一个扩展来为您执行此操作：

extension Double {
    func decimalRounded(to scale: Int = 2, roundingMode: NSDecimalNumber.RoundingMode = .plain) -> Decimal {
        var newValue: Decimal = 0
        var currentValue = Decimal(self)
        
        NSDecimalRound(&newValue, &currentValue, scale, roundingMode)
    
        return newValue
    }
}

然后：

var myMoney = Money()
myMoney.amount = 10.019999999999997952.decimalRounded(roundingMode: .down)
print(myMoney.amount)