How to Convert a Go Slice to an Array?

Converting Slice to Array in Go

In Go, attempting to assign a slice to an array directly will result in a compilation error. This question explores how to convert slices of specific lengths into arrays.

Problem Statement

Consider a struct defining a lead block with a Magic field consisting of an array of 4 bytes:

type Lead struct {
  Magic        [4]byte
  Major, Minor byte
  Type         uint16
  Arch         uint16
  Name         string
  OS           uint16
  SigType      uint16
}

The task is to assign a slice of 4 bytes to the Magic field using the following syntax:

lead := Lead{}
lead.Magic = buffer[0:4] // Attempt to assign slice to array

Solution

To convert a slice of a specified length into an array, Go provides the following methods:

Using copy() with Array Subslice

The built-in copy function can be tricked into copying a slice to an array by treating the array as a slice:

copy(varLead.Magic[:], someSlice[0:4])

Using For Loop

Iterate over the slice elements and assign them to the array elements:

for index, b := range someSlice {
    varLead.Magic[index] = b
}

Using Array Literals

An alternative approach is to use array literals directly:

type Lead struct {
  Magic        [4]byte
  Major, Minor byte
  Type         uint16
  Arch         uint16
  Name         string
  OS           uint16
  SigType      uint16
}

lead := Lead{Magic: [4]byte{0x12, 0x34, 0x56, 0x78}}

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