What is difference between “?” and “!” in Swift?

Question

I know what \"?\" and \"!\" mean when I declare variables in Swift. But what do they mean when using these variables? For example, in this code:

var         


        

Answer 1

what is ! and ?:

• Use ? if the value can become nil in the future, so that you test for this.
• Use ! if it really shouldn't become nil in the future, but it needs to be nil initially.

if You are using attachment.image!.size any variable with ! means, compiler don't bother about that variable has any value or nil. it goes to take action further, it will here try to get size of image. if attachment.image is nil then app will be crash here.

While, attachment.image?.size, this will make sure you, if attachment.image isn't nil then further action will be take place, otherwise But it confirm Application will not be crash in case of nil value of image .

Summary:

We should have to use !, when we make sure option type variable has value at a time and we need to take action on it further, Otherwise.