try

You have 2 options when you try calling a function that may throw.

You can take responsibility of?handling errors?by surrounding your call within a do-catch block:

Or just try calling the function,and?pass the error along?to the next caller in the call chain:

try!

What happens when you try to access an implicitly unwrapped optional with a nil inside it? Yes,true,the app will CRASH! Same goes with try! it basically ignores the error chain,and declares a “do or die” situation. If the called function didn’t throw any errors,everything goes fine. But if it failed and threw an error,?your application will simply crash.

try?

A new keyword that was introduced in Xcode 7 beta 6. It?returns an optional?that unwraps successful values,and catches error by returning nil.

Or we can use new awesome guard keyword:

One final note here,by using?try??note that you’re discarding the error that took place,as it’s translated to a nil. Use try? when you’re focusing more on successes and failure,not on why things failed.

?

https://stackoverflow.com/questions/32390611/try-try-try-what-s-the-difference-and-when-to-use-each