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。
像这样:
5+4+MYVAR*5
我想用自定义Double值替换此MYVAR字符串。
如果不存在,我将使用循环和类似方法,但希望有一个内置的(并且更快)的解决方案。
谢谢。
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