A quick note to say that I’m taking next week off, for a move. I expect to return October 4 with more Boldy Go: Daily emails. Until then!

We’re down to the final two built-in functions in Go. And these are probably functions you should not be using, except possibly in throw-away test code or during debugging.

Bootstrapping

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

Implementation restriction: print and println need not accept arbitrary argument types, but printing of boolean, numeric, and string types must be supported.

So if you’re not supposed to use these, why do they exist? And what should you use instead?

Well, as the section title implies, these functions exist largely for historical reasons, and were used during the bootstrapping of the language. Before the fmt package existed (more on that in a moment), it was handy to have a simple way to print out debug messages. Thus print and println. They’re still often useful for such things. Especially if you don’t want to bloat your code by importing fmt—a concern mostly reserved for embedded systems, since it’s otherwise virtually impossible to build a Go program that doesn’t import fmt.

So what do you use instead? The fmt package provides a number of alternatives, which are much more flexible and appropriate for normal use.

fmt.Print and fmt.Println are the direct replacements for print and println, respectively:

fmt.Print("Hello, ")
fmt.Println("世界", 123, true)
print("Hello, ")
println("世界", 123, true)

outputs:

Hello, 世界 123 true
Hello, 世界 123 true

Addtionally, the fmt family of functions support many more types than the built-in functions do:

var x struct{}
fmt.Print(x) // {}
print(x)     // illegal types for operand: print struct {}

What’s more, these functions could, in theory, be removed from the language in the future. So best not to rely on them. 😁

Quotes from The Go Programming Language Specification Language version go1.23 (June 13, 2024)