表达式中的NSExpression自定义变量 [英] NSExpression custom variables inside expression

问题描述

最近我发现了NSExpression类，我想知道是否有可能评估表达式中的自定义变量。

这样的一个例子：

  5 + 4 + MYVAR * 5 
  

如果这不存在，我会用循环和类似的，但希望那里

谢谢。

解决方案

$ pre $ let myInt = 4
let myFormulaInt =5 + 4 + myInt * 5
let intElements = [myInt：myInt]

let myResultInt = NSExpression（format：myFormulaInt）.expressionValueWithObject（intElements，context：nil）.integerValue

println（myResultInt）// 29


let myDouble = 2.5
let myFormulaDouble =5 + 4 + myDouble * 5
let doubleElements = [myDouble：myDouble]

let myResultDouble = NSExpression（format： MYF ormulaDouble）.expressionValueWithObject（doubleElements，context：nil）.doubleValue

println（myResultDouble）// 21.5


Xcode 8 GM•Swift 3

  let myInt = 4 
 let myFormulaInt =5 + 4 + myInt * 5
 let intElements：[String：Int] = [myInt：myInt] 
 
 let myResultInt = NSExpression（format：myFormulaInt ）.expressionValue（with：intElements，context：nil）as！ Int 
 
 print（myResultInt）// 29 
 
 
 let myDouble = 2.5 
 let myFormulaDouble =5 + 4 + myDouble * 5
 let doubleElements：[String：Double] = [myDouble：myDouble] 
 
 let myResultDouble = NSExpression（format：myFormulaDouble）.expressionValue（with：doubleElements，context：nil）as！ Double 
 
 print（myResultDouble）// 21.5 
  

Recently I have discovered NSExpression class and I am wondering is there a possibility to evaluate custom variables inside expression.

Something like this:

5+4+MYVAR*5

I would like to replace this MYVAR string with custom Double value.

If this don't exists, I will go with loops and similar, but hoping that there is a built-in (and faster) solution.

Thanks.

解决方案

let myInt = 4
let myFormulaInt = "5 + 4 + myInt * 5"
let intElements = ["myInt": myInt]

let myResultInt = NSExpression(format: myFormulaInt).expressionValueWithObject(intElements, context: nil).integerValue

println(myResultInt)   // 29


let myDouble = 2.5
let myFormulaDouble = "5 + 4 + myDouble * 5"
let doubleElements = ["myDouble": myDouble]

let myResultDouble = NSExpression(format: myFormulaDouble).expressionValueWithObject(doubleElements, context: nil).doubleValue

println(myResultDouble)   // 21.5

Xcode 8 GM • Swift 3

let myInt = 4
let myFormulaInt = "5 + 4 + myInt * 5"
let intElements: [String:Int] = ["myInt": myInt]

let myResultInt = NSExpression(format: myFormulaInt).expressionValue(with: intElements, context: nil) as! Int

print(myResultInt)   // 29


let myDouble = 2.5
let myFormulaDouble = "5 + 4 + myDouble * 5"
let doubleElements: [String: Double] = ["myDouble": myDouble]

let myResultDouble = NSExpression(format: myFormulaDouble).expressionValue(with: doubleElements, context: nil) as! Double

print(myResultDouble)   // 21.5

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