What size of memory does an empty structure occupy in Go language?

An empty struct in Go occupies 0 bytes. This is because it contains no fields and therefore does not require memory allocation for storage. The address of an empty struct exists, but it is the same for all empty structs.

Example:

package main

import (
	"fmt"
	"unsafe"
)

func main() {
	type Empty struct{} // Declare an empty struct

	var e Empty
	fmt.Printf("Size of empty struct: %d bytes\n", unsafe.Sizeof(e)) // Print size
	fmt.Printf("Address of empty struct: %p\n", &e) // Print address

	var e2 Empty
	fmt.Printf("Address of another empty struct: %p\n", &e2) // Address will be the same

	s := make([]Empty, 10) // Slice of empty structs
	fmt.Printf("Size of slice of 10 empty structs: %d bytes\n", unsafe.Sizeof(s)) // Size of slice (descriptor)

	s2 := make([]Empty, 0, 10) // Slice of 0 empty structs with capacity 10
	fmt.Printf("Size of slice of 0 empty structs with capacity 10: %d bytes\n", unsafe.Sizeof(s2)) // Size of slice (descriptor)
}

Program output:

Size of empty struct: 0 bytes
Address of empty struct: 0x10dbf58
Address of another empty struct: 0x10dbf58
Size of slice of 10 empty structs: 24 bytes
Size of slice of 0 empty structs with capacity 10: 24 bytes

Note that the size of the slice does not depend on the number of empty structs inside, as the slice itself is a structure (descriptor) containing a pointer to the underlying array, length, and capacity.