Arrays

• Fixed size, cannot be changed. From a syntax standpoint, this is what separates it from slices.
• The size is part of the type definition. [5]int != [4]int
• An array is a value, passing it around means copying the value (unlike C where an array is a pointer to the first element in memory). Can create pointers to arrays and pass it around for the same effect.

  a := [5]int
  b := [10]SomeStruct
  c :=[...]int{1,2,3}  // but this is a slice --> c:=[]int{12,13,14,15}

Slices

• Slices are references to arrays, built on top of array
• Size is not fixed and can be increased using the append built-in function
• Syntatically the difference between a slice and array is omitting the size or ... in the definition

Slicing

• You can create a new slice by “slicing” an existing slice or array
• An important point to remember is when “sliced” the new slice shares the underlying storage

first := []byte{'g','o','l','a','n','g'}
second := first[1:3]
fmt.Printf("%s\n",first) // golang
fmt.Printf("%s\n",second) // ol

second[1]='X'
fmt.Printf("%s\n",first) // goXang
fmt.Printf("%s\n",second) // oX

References

• https://blog.golang.org/slices-intro
• https://blog.golang.org/slices
• https://research.swtch.com/godata
• https://www.openmymind.net/The-Minimum-You-Need-To-Know-About-Arrays-And-Slices-In-Go/
• https://blog.fraixed.es/post/golang-slices-structs-or-pointers-to-structs-dilemma/

Maps

• Valid keys - comparable types: boolean, numeric, string, pointer, channel, and interface types, and structs or arrays that contain only those types

Initialising

var m map[string]int

• Map types are reference types, like pointers or slices, and so the value of m above is nil; it doesn’t point to an initialized map

• Initialise a nil map with make m := make(map[string]int)

Getting and setting

• a := m[“doesntexist”] - a will be assigned the “zero value” of that type
• a, ok := m[“doesntexist”] - ok will be assigned false
• , ok := m[“doesntexist”]- same thing as above
• m[“exists”] = 1

Deleting

• delete(m, “exists”)

Iterating

• for k, v := range m {}

References

• Go maps in action - The Go Blog

FAQ

• Should you create an array of pointers. For example, which is better?

  sayans := []*Sayan{
    &Sayan{Name: "Goku", Power: 9001,}
  }