Can you evaluate a string in Swift?

Question

I have a variable and I have a function stored in it as a string:

var x = "func myFunction(y :Int) {println(y)}"

Is there a way to evaluate the string and run the function?

Humid

Answer 1

No.

There is no equivalent of eval() in JavaScript or ScriptEngine in Java for Swift.

A common use for string evaluation is mathematical expressions; if you want to evaluate these, you can use NSExpression.valueWithExpression(format: String):

let stringWithMathematicalOperation: String = "5*5" // Example
let exp: NSExpression = NSExpression(format: stringWithMathematicalOperation)
let result: Double = exp.expressionValue(with:nil, context: nil) as! Double // 25.0

Hotheaded

This does crash when you perform mod operation. 10%20 it will crash. – Persuasion

I am trying to use that for formulas, but when I divide multiply and power it gives me a strange number that don’t correspond to the correct result – Gob

My problem was related with the comma format, after change it everything works great. – Gob

Answer 2

Yes, and if string contains boolean expression then also this can be evaluated. I've done it something like this,

let stringWithMathematicalOperation: String = "true && false "
let exp: NSExpression = NSExpression(format: stringWithMathematicalOperation)
let result: Bool = exp.expressionValueWithObject(nil, context: nil) as Bool // Answer: false

Pfeifer