Swift? And! Swift understanding

Swift? And! Swift understanding
Swift? And! Understanding

The Swift language uses var to define variables, but unlike other languages, Swift does not automatically assign an initial value to the variables, that is, the variables do not have a default value. Therefore, you must initialize the variables before using them.

• "?"
  Start with "?" Yes

Let str = strValue ?. Length

? This example indicates that strValue may be nil, and when strValue is nil, the subsequent length will not be called, increasing the code security.

• "!"
  Let's talk about this.
  This is equivalent to the above negative, which means something positive.
  Let str = strValue !. Length

  It means that strValue must be non-nil, so it can be directly added!