Go - (6) Arrays and Slices

Arrays

• In Go, arrays have a fixed size.

var marks [10]int // an array of 10 integers

Assigning values to an array looks like this.

names := [3]string{
    "Edward",
    "Bella",
    "Jcob",
}

In Go, if you assign an array to another array, it copies all the elements of the first array. Also, when you pass an array to a function, it gets a copy of the array.

But what if you want to allocate size dynamically?

Slice

• Built on top of arrays.
• Holds a reference to the underlying array.
• Dynamically-sized
• In Go, we work with slices 90% of the time.

Unlike assigning an array to another array, when you assign a slice to another slice, both points to the same array. This gives pointer-like behaviour.

sliceA := make([]int, 4, 8)
sliceFixed := make([]string, 5)
sliceLiteral := []string{"hello", "hi", "thanks"}

Capacity of a slice is the maximum length it can take. If the data exceeded the capacity, the slice is reallocated. You can get the capacity of a slice using the cap() function.

Length is the current length (number of elements) a slice has. You can get the length of a slice using the len() function.

In the above example, sliceA is an int slice, which is 4 in length but has a capacity of 8. Both the length and capacity of the sliceFixed size are 5. Also, if you print the length of sliceLiteral, it will give 3.

Variadic functions

• A function that can take an arbitrary number of final arguments.

Check the example below. The printNames() function takes the names argument, which is a slice. You can see it in the main function where we call the printNames(). Note that we can pass a slice any number of string elements.

func printNames(names ...string) {
    // names is a slice
    for i := 0; i < len(names); i++ {
        fmt.Println(names[i])
    }
}

func main() {
    users := []string{"edward", "jcob", "bella"}
    printNames(users...)
}

Instead of a for loop, you can use range to print elements of a slice.

func printSweets() {
    sweets := []string{"cake", "chocolate", "toffee", "macrons"}
    for _, s := range sweets {
        fmt.Println(s)
    }
}

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