What is in Swift

Variables are used to store data in memory so that we can use them in program . Variables are like container that can hold data which can be changed later. Every variable has a unique name called identifier.

Omitting Argument Labels If you don’t want an argument label for a parameter, write an underscore ( _ ) instead of an explicit argument label for that parameter. // refer to the argument values for the first and second parameters.

In the documentation it is being used as a wildcard to indicate a function that takes an unnamed parameter .

The _ is a placeholder for the parameter name . In your example, you call them differently, in the second function, you need to write the parameter name a: 1 . Swift’s function name convention is funcName(param1:param2:) , and it needs the _ as a placeholder to create the name of the function.