How Does Go\'s `copy()` Function Work With Overlapping Slices?

Copy Function Explained: A Comprehensive Guide

The copy function in Go is used to duplicate elements from a source slice to a destination slice. It takes two parameters: a destination slice and a source slice, both of which must have the same element type.

How copy() Works

copy() copies elements from the source slice to the destination slice, but only up to the minimum length of the two slices. If the source slice is shorter than the destination slice, only the elements in the source slice are copied. Conversely, if the destination slice is shorter than the source slice, only the first len(dst) elements are copied.

An important aspect of copy() is that it can handle overlapping slices. That is, it can copy elements from a source slice to a destination slice that shares the same underlying array. This can be useful for operations like shifting elements or rearranging slices.

Use Case Examples

Below are a few examples of how copy() can be used:

• Creating a copy of a slice:

  <code class="go">src := []int{10, 11, 12, 13, 14}
  dst := make([]int, len(src))
  n := copy(dst, src)
  fmt.Println("n =", n, "src =", src, "dst =", dst)</code>

  Output:

  n = 5 src = [10 11 12 13 14] dst = [10 11 12 13 14]

• Copying a portion of a slice:

  <code class="go">src := []int{10, 11, 12, 13, 14}
  dst := make([]int, 2)
  n := copy(dst, src[1:])
  fmt.Println("n =", n, "src =", src, "dst =", dst)</code>

  Output:

  n = 2 src = [10 11 12 13 14] dst = [11 12]

• Overlapping slices:

  <code class="go">src := []int{10, 11, 12, 13, 14}
  dst := src[1:]
  n := copy(dst, src)
  fmt.Println("n =", n, "src =", src, "dst =", dst)</code>

  Output:

  n = 4 src = [10 11 12 13 14] dst = [11 12 13 14]

Special Case: Copying from a String to a Byte Slice

copy() can also be used to copy bytes from a string to a slice of bytes. This is useful for converting strings to byte arrays or for working with byte data.

For example:

<code class="go">str := "Hello, World!"
data := make([]byte, 5)
n := copy(data, str)
fmt.Println("n =", n, "str =", str, "data =", data)</code>

Output:

n = 5 str = Hello, World! data = [72 101 108 108 111]

Conclusion

The copy function in Go is a versatile tool for working with slices. It provides a concise and efficient way to duplicate slices, copy portions of slices, and even handle overlapping slices. Understanding how copy() works is essential for effective slice manipulation in Go.

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