Swift inserted in the string at the specified location String

api:

str.index(<#T##i: String.Index##String.Index#>, offsetBy: <#T##String.IndexDistance#>)

Roughly explain

str.endIndex what position from the beginning

offsetBy: offset number bit, uh .. ± represents the direction

 

 

 

A little bit of progress every day, I pay homage to wasted time!