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Have you ever tried to explain an “if” statement in as few words as possible? It’s such a simple concept, that I don’t think I’ve ever bothered trying to explain it.

Well, today’s section of the Go spec does explain it. And I have to say, I think it does an admirable job.

If statements

“If” statements specify the conditional execution of two branches according to the value of a boolean expression. If the expression evaluates to true, the “if” branch is executed, otherwise, if present, the “else” branch is executed.

I suppose in my head, an if statement is separate from an else, and this would lead to some confusion in trying to explain the concept. But I like this explanation. By framing it as either executing one branch or the other, it’s quite simple. Then the second branch (the one prefaced by else) is made optional.

IfStmt = "if" [ SimpleStmt ";" ] Expression Block [ "else" ( IfStmt | Block ) ] .

if x > max {
	x = max
}

Relative to some other languages, that have elseif, Go makes this very simple and straight forward. Although one might wonder how to handle the else … if case in Go. Well, you just do it like that:

if thing == 1 {
	/* ... */
} else if thing == 2 {
	/* ... */
} else if thing == 3 {
	/* ... */
}

This is roughly equivalent to:

if thing == 1 {
	/* ... */
} else {
	if thing == 2 {
		/* ... */
	} else {
		if thing == 3 {
			/* ... */
		}
	}
}

And I think when you consider it this way, it’s pretty intuitive, and removes whatever mystery might exist by thinking of if as a combination of if, else, and elseif interactions.

The expression may be preceded by a simple statement, which executes before the expression is evaluated.

if x := f(); x < y {
	return x
} else if x > z {
	return z
} else {
	return y
}

I’m sure you’ve seen these simple statements before; they’re allowed with certain if, select, and switch statements. They let you do a little pre-computation, within the scope of that statement. That is to say, that the following are roughly equivalent, in terms of variable scoping:

if x := f; x < y {
	return x
}

{
	x := f
	if x < y {
		return x
	}
}

Quotes from The Go Programming Language Specification Language version go1.22 (Feb 6, 2024)