Behavior of Go print functions

This page exists because:

• I've been using this language for more than a decade and still can't remember this.
• The documentation is full of annoying "x is like y" redirects.
• Just using Printf everywhere feels like a cop-out.

Function	Spaces	Newline	Documentation
fmt.Print	no	no
fmt.Fprint	no	no
fmt.Sprint	no	no
fmt.Println	yes	yes
fmt.Fprintln	yes	yes
fmt.Sprintln	yes	yes
log.Print	no	yes	…in the manner of fmt.Print
log.Fatal	no	yes	…equivalent to Print() followed by a call to os.Exit(1)
log.Panic	no	yes	…equivalent to Print() followed by a call to panic()
log.Println	yes	yes	…in the manner of fmt.Println
log.Fatalln	yes	yes	…equivalent to Println() followed by a call to os.Exit(1)
log.Panicln	yes	yes	…equivalent to Println() followed by a call to panic()
testing.T.Log	yes	yes	…analogous to Println
testing.T.Error	yes	yes	…equivalent to Log followed by Fail
testing.T.Fatal	yes	yes	…equivalent to Log followed by FailNow

"Spaces" describes whether spaces are always added between operands, or only when neither is a string.

"Newline" describes whether a trailing newline is added.

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To summarize:

• ln functions add spaces and a trailing newline.
• Non-ln functions don't add spaces or a trailing newline.

So you should write code like this:

fmt.Println("Something failed:", err)
fmt.Fprintln(os.Stderr, "Something failed:", err)

Except the log functions always add newlines, even for the non-ln versions. So you can write:

log.Print("Something failed: ", err)
log.Fatal("Something failed: ", err)

Or (at the expense of an additional character):

log.Println("Something failed:", err)
log.Fatalln("Something failed:", err)

Except the testing functions always add spaces and append newlines, despite not having ln in their names. So write:

t.Error("Something failed:", err)
t.Fatal("Something failed:", err)

There's always Go 2, I guess.