I am new a Golang programmer and I see code snippets were functions return err as last argument a lot of time.
f, err := strconv.ParseFloat(asciiFloat, 64)
Question is must all functions be made to return err even if no error handling is involved in the function implementation. And how will I know a function is or is not returning an err value?
Must I checkout docs every time I need to use a function?
Answering your question: Fortunately, Go prevents certain types of programmers errors. It just won't let you compile the program if you forget one of the values that the function returns.
It's a good practice to return errors in Go, read Errors section of Effective Go
Library routines must often return some sort of error indication to the caller. As mentioned earlier, Go's multivalue return makes it easy to return a detailed error description alongside the normal return value. It is good style to use this feature to provide detailed error information.
In Go, error handling is important. The language's design and conventions encourage you to explicitly check for errors where they occur
However there is a problem described here and probably will be improved in Go 2
In general Go programs have too much code checking errors and not enough code handling them.
Dave Cheney writes in the blog
I’m suggesting changing your code so you don’t have as many errors to handle.
must all functions be made to return err
No.
But in case you function may return error - you have to return this error as last value.
It's good practice to return error as last value.
how will I know a function is or is not returning an err
Before using some function you have to see that function and in declaration you'll see what function returns. Also it's good to read documentation to function, and check out how to use function.