Difference between fmt.Println() and println() in Go

Question

As illustrated below, both fmt.Println() and println() give same output in Go: Hello world!

But: how do they differ from each

Answer 1

To build upon nemo's answer:

println is a function built into the language. It is in the Bootstrapping section of the spec. From the link:

Current implementations provide several built-in functions useful during bootstrapping. These functions are documented for completeness but are not guaranteed to stay in the language. They do not return a result.

Function   Behavior

print      prints all arguments; formatting of arguments is implementation-specific
println    like print but prints spaces between arguments and a newline at the end

Thus, they are useful to developers, because they lack dependencies (being built into the compiler), but not in production code. It also important to note that print and println report to stderr, not stdout.

The family provided by fmt, however, are built to be in production code. They report predictably to stdout, unless otherwise specified. They are more versatile (fmt.Fprint* can report to any io.Writer, such as os.Stdout, os.Stderr, or even a net.Conn type.) and are not implementation specific.

Most packages that are responsible for output have fmt as a dependency, such as log. If your program is going to be outputting anything in production, fmt is most likely the package that you want.