Predeclared identifiers

The following identifiers are implicitly declared in the universe block:

Types:
	any bool byte comparable
	complex64 complex128 error float32 float64
	int int8 int16 int32 int64 rune string
	uint uint8 uint16 uint32 uint64 uintptr

Constants:
	true false iota

Zero value:
	nil

Functions:
	append cap close complex copy delete imag len
	make new panic print println real recover


Perhaps confusingly, any of these can be shadowed.  That is, you can bind these names to your own variables, constants, functions, etc.  However, you _shouldn't_.

```golang
func main() {
	var s = []int{1, 2, 3}
	fmt.Println(len(s))
}

func len(any) int { // Never, ever do this!!!
	return -1000
}

When Go 1.21 is released, presumably in August, this list will be extended to include three new functions: min, max, and clear.

Quotes from The Go Programming Language Specification Version of December 15, 2022

Related Content

The concept of shadowing should be familiar to many readers. But here we see how Go defines it… Declarations and scope … An identifier declared in a block may be redeclared in an inner block. While the identifier of the inner declaration is in scope, it denotes the entity declared by the inner declaration. Notice that shadowing is not limited to variables. You can shadow function names, types, constants, or variables.

The universe and package blocks

Let’s now dive into the specific scoping rules in Go. There are 8 rules here, and we’ll take one or two per day… Declarations and scope … Go is lexically scoped using blocks: The scope of a predeclared identifier is the universe block. The “universe block”, which encompasses all Go source text, only contains the predeclared identifiers defined in the specification. Specifically, these identifiers are the names of predeclared types, the constants true, false, and iota, the zero value nil, and the built-in functions.

Dependency pinning

Today I want to share a trick I stumbled upon. It won’t matter to most of you. If it does matter to you, it will probably save you a bunch of headaches! First, some background. Have you ever had to use an outdated dependency for $REASONS? If not, you can skip today’s email, unless you’re just curious. One of my clients is still using MongoDB 3.2. MongoDB was EOLed more than a year before anyone had ever heard the term “COVID”.

Predeclared identifiers

July 5, 2023