What's the Difference Between `struct{}` and `struct{}{} `in Go?

Delving into the Nature of struct{} and struct{}{} in Go

Go leverages the concept of structs to define sequences of named elements. While struct{} and struct{}{} may seem similar, they possess subtle distinctions.

struct{}: The Zero-Sized Empty Struct

A struct{} represents a struct with no defined elements. It exists primarily to hold no data. Its diminutive size enables efficient memory utilization without requiring additional space.

struct{}: A Composite Literal for the Empty Struct

In contrast, struct{}{} constructs a value of type struct{}. Its syntax features the struct type followed by empty braces, as no fields exist.

Leveraging struct{} in Practice: Creating a Set

Go inherently lacks a set data structure, but maps offer a viable alternative. By defining a map's value type as struct{}, we create a set analogue that stores only keys. This technique maintains the unicity of keys within the map.

For instance:

var set map[string]struct{}
set = make(map[string]struct{})
set["red"] = struct{}{}
set["blue"] = struct{}{}
_, ok := set["red"]
fmt.Println("Is red in the map?", ok)

The map functionality showcases the presence or absence of keys, mimicking set behavior.

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