将Swift字符串公式转换为实数计算 [英] Swift string formula into a real calculation

问题描述

我有几个公式存储在Plist中，例如A * B.我试图找出如何将此公式当前存储为Plist中的字符串并将其用作实际计算公式。我尝试将制定公式的路线设置为\（A）* \（B），然后在尝试使用公式之前设置A和B，但它不起作用。有什么建议吗？

I have several formulas stored in a Plist such as A * B. I'm trying to figure out how I could take this formula currently stored as a string in a Plist and use it as an actual calculation formula. I tried going the route of making the formula to \(A) * \(B) and then setting A and B before trying to use the formula but it did not work. Any suggestions?

示例

let A = 5
let B = 2

println (formula)

实际打印出来 \（A）* \（B）

actually printed out "\(A) * \(B)"

推荐答案

Xcode 8.3.1•Swift 3.1

extension String {
    var expression: NSExpression {
        return NSExpression(format: self)
    }
}

let a = 5
let b = 2
let intDictionary = ["a": a,"b": b]

var formula = "a * b"
if let timesResult = formula.expression.expressionValue(with: intDictionary, context: nil) as? Int {  
    print(timesResult) // 10
}
formula = "(a + b) / 2"
if let intAvgResult = formula.expression.expressionValue(with: intDictionary, context: nil) as? Int {
    print(intAvgResult)    // 3
}



let x = 5.0
let y = 2.0
let z = 3.0

let doubleDictionary = ["x": x, "y": y, "z": z]


formula = "(x + y + z) / 3"
if let doubleAvgResult = formula.expression.expressionValue(with: doubleDictionary, context: nil) as? Double {
    print(doubleAvgResult)
}

这篇关于将Swift字符串公式转换为实数计算的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！