9-slice.md

This Go program is a tutorial that demonstrates various concepts related to slices, a dynamic array-like data structure in Go. The code covers topics such as slice creation, modification, appending, copying, and working with two-dimensional slices.

Below is a detailed explanation of the code:

package main

import (
   "fmt"
   "slices"
)

func main() {

   // Declare an uninitialized slice of strings
   var s []string

   // Print the uninitialized slice, its nil status, and its length
   fmt.Println("uninit:", s, s == nil, len(s) == 0) // Output: uninit: [] true true

   // Create an empty slice of strings with a length of 3 and a capacity of 3
   s = make([]string, 3)
   fmt.Println("emp:", s, "len:", len(s), "cap:", cap(s)) // Output: emp: [   ] len: 3 cap: 3

   // Set values for the first three elements of the slice
   s[0] = "a"
   s[1] = "b"
   s[2] = "c"
   fmt.Println("set:", s) // Output: set: [a b c]

   // Access the third element of the slice
   fmt.Println("get:", s[2]) // Output: get: c

   // Print the length of the slice
   fmt.Println("len:", len(s)) // Output: len: 3

   // Append new elements to the slice
   s = append(s, "d")
   s = append(s, "e", "f")
   fmt.Println("apd:", s) // Output: apd: [a b c d e f]

   // Create a new slice `c` with the same length as `s` and copy elements from `s` to `c`
   c := make([]string, len(s))
   copy(c, s)
   fmt.Println("cpy:", c) // Output: cpy: [a b c d e f]

   // Slice a portion of `s` from index 2 (inclusive) to index 5 (exclusive)
   l := s[2:5]
   fmt.Println("sl1:", l) // Output: sl1: [c d e]

   // Slice `s` from the beginning (inclusive) to index 5 (exclusive)
   l = s[:5]
   fmt.Println("sl2:", l) // Output: sl2: [a b c d e]

   // Slice `s` from index 2 (inclusive) to the end
   l = s[2:]
   fmt.Println("sl3:", l) // Output: sl3: [c d e f]

   // Declare and initialize a slice `t` with values in a single line
   t := []string{"g", "h", "i"}
   fmt.Println("dcl:", t) // Output: dcl: [g h i]

   // Declare another slice `t2` with the same values as `t`
   t2 := []string{"g", "h", "i"}

   // Use the `slices.Equal` function to check if `t` and `t2` are equal
   if slices.Equal(t, t2) {
       fmt.Println("t == t2") // Output: t == t2
   }

   // Create a 2-dimensional slice of integers
   twoD := make([][]int, 3)
   for i := 0; i < 3; i++ {
       innerLen := i + 1
       twoD[i] = make([]int, innerLen)
       for j := 0; j < innerLen; j++ {
           twoD[i][j] = i + j
       }
   }
   fmt.Println("2d: ", twoD) // Output: 2d:  [[0] [1 2] [2 3 4]]
}

Output

uninit: [] true true
emp: [  ] len: 3 cap: 3
set: [a b c]
get: c
len: 3
apd: [a b c d e f]
cpy: [a b c d e f]
sl1: [c d e]
sl2: [a b c d e]
sl3: [c d e f]
dcl: [g h i]
t == t2
2d:  [[0] [1 2] [2 3 4]]

Let's break down the code step by step:

1. Package Import:

   package main
   
   import (
       "fmt"
       "slices"
   )

   • The main package is the entry point for the executable.
   • It imports the "fmt" package for formatted I/O and a custom "slices" package (presumably defined elsewhere) for a function called Equal.

2. Main Function:

   func main() {
       // ...
   }

   • The main function is the starting point of the program.

3. Slice Declaration and Initialization:

   var s []string
   fmt.Println("uninit:", s, s == nil, len(s) == 0)
   
   s = make([]string, 3)
   fmt.Println("emp:", s, "len:", len(s), "cap:", cap(s))

   • Declares an uninitialized slice s and prints its properties.
   • Initializes s with a length of 3 using make, and prints the slice along with its length and capacity.

4. Slice Modification:

   s[0] = "a"
   s[1] = "b"
   s[2] = "c"
   fmt.Println("set:", s)
   fmt.Println("get:", s[2])
   fmt.Println("len:", len(s))

   • Sets values in the slice s, prints the modified slice, retrieves and prints an element, and prints the length of the slice.

5. Slice Appending:

   s = append(s, "d")
   s = append(s, "e", "f")
   fmt.Println("apd:", s)

   • Appends elements "d", "e", and "f" to the slice s using the append function, and prints the resulting slice.

6. Slice Copying:

   c := make([]string, len(s))
   copy(c, s)
   fmt.Println("cpy:", c)

   • Creates a new slice c with the same length as s using make.
   • Copies the elements of s to c using the copy function and prints the copied slice.

7. Slice Slicing:

   l := s[2:5]
   fmt.Println("sl1:", l)
   
   l = s[:5]
   fmt.Println("sl2:", l)
   
   l = s[2:]
   fmt.Println("sl3:", l)

   • Demonstrates various ways to create sub-slices of the original slice s and prints the results.

8. Slice Declaration and Initialization with Literal Values:

   t := []string{"g", "h", "i"}
   fmt.Println("dcl:", t)

   • Declares and initializes a slice t with literal values "g", "h", and "i", and prints the slice.

9. Custom Slice Equality Check:

   t2 := []string{"g", "h", "i"}
   if slices.Equal(t, t2) {
       fmt.Println("t == t2")
   }

   • Uses a custom function Equal from the "slices" package to check if slices t and t2 are equal and prints a message accordingly.

10. Two-Dimensional Slice:

    twoD := make([][]int, 3)
    // ... (nested loop to initialize values)
    fmt.Println("2d: ", twoD)

    • Creates a two-dimensional slice twoD with three inner slices.
    • Initializes values in the two-dimensional slice using a nested loop.
    • Prints the two-dimensional slice.

This tutorial covers fundamental concepts related to slices in Go, including creation, modification, appending, copying, slicing, and working with two-dimensional slices. The custom Equal function demonstrates how you can extend functionality by creating your own utility functions.