swift func: i can't understand underscore as a parameter name that can compile -

how use underscore parameter

func test(currentname name: string, _: int) {      print("aa\(name) abc");     //how use  _  parameter? }  test(currentname:"aa", 3)

_ means when call test function, don't have write text before second parameter test(currentname:"aa", 3)

if declare function this:

func test(currentname name: string, secondparameter: int) {         print("aa\(name) abc");     //how use  _  parameter? }

then when call test function, must call this:

test(currentname:"aa", secondparameter: 3)

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