How to get nil if something can't be evaluated?

Question

I am using NSExpression to solve strings from user input. Here is the code

var userInput = "5+"
var solveUserInput = NSExpression(format: "\(userInput)")

It will crash my program because it can't solve it, but what I want to do is to return nil if the string is unsolvable by NSExpression. Is there any way to do this?

Look [here](http://stackoverflow.com/questions/28005595/handle-nsinvalidargumentexception-exception-from-nsexpression-with-swift?lq=1) and [here](http://stackoverflow.com/questions/24710424/catch-an-exception-for-invalid-user-input-in-swift). — Mario Zannone, Jul 09 '15 at 08:54

score 1 · Accepted Answer · answered Jul 09 '15 at 09:52

1

NSExpression is not really meant for that kind of usage (evaluation of user input).

I suggest that you have a look at DDMathParser instead.

answered Jul 09 '15 at 09:52

Mario Zannone

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That surprises me. I am using it in a small project of mine, with no problem. – Mario Zannone Jul 09 '15 at 14:21
If you want to look at it then go to this link http://stackoverflow.com/questions/31168751/mathematical-parser-in-swift – Epic Defeater Jul 09 '15 at 14:23
Thanks for your comment up there because it helped me a lot – Epic Defeater Jul 09 '15 at 14:51
I guess your comment is ironic ;-) If you can reproduce the issue in a minimal Xcode project and publish the project somewhere, I will be happy to have a look at it. – Mario Zannone Jul 09 '15 at 15:22

How to get nil if something can't be evaluated?

1 Answers1