How Do I Efficiently Convert a Go Array to a Slice?

Converting Arrays to Slices in Go

When working with data in Go, it's often necessary to convert between arrays and slices. The primary distinction between the two is that arrays have a fixed size, while slices are dynamic and can be resized as needed. This can lead to confusion when trying to pass data between functions that expect different types.

Converting from Array to Slice

Suppose you have a function that returns an array:

func Foo() [32]byte {...}

And you need to pass that result to another function that expects a slice:

func Bar(b []byte) { ... }

Simply assigning the array to a slice won't work as shown below:

d := Foo()
Bar(d)

This will result in the error "cannot convert d (type [32]byte) to type []byte".

The Correct Solution

The correct approach is to use the slicing syntax array[:] to extract a slice from the array:

x := Foo()
Bar(x[:])

This syntax creates a slice that references the underlying array data without creating a copy. This is crucial for efficient data transfer, especially when dealing with large buffers.

Here's a full working example:

package main

import (
    "fmt"
)

func Foo() [32]byte {
    return [32]byte{'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'}
}

func Bar(b []byte) {
    fmt.Println(string(b))
}

func main() {
    x := Foo()
    Bar(x[:])
}

By following this approach, you can seamlessly convert arrays to slices in Go without sacrificing performance or introducing unnecessary data copies.

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