slice = append(slice, "hello", "world")

slice1 := []string{"!"}
slice2 := []string{"Hello", "world"}
slice  := append(slice1, slice2...)

Run in the Go Playground

If you need to remove one or more elements from a slice, or if you need to work with a sub slice of another existing one; you can use the following method.

Following examples uses slice of int, but that works with all type of slice.

So for that, we need a slice, from witch we will remove some elements:

slice := []int{1, 2, 3, 4, 5, 6} 
// > [1 2 3 4 5 6]

We need also the indexes of elements to remove:

// index of first element to remove (corresponding to the '3' in the slice)
var first = 2

// index of last element to remove (corresponding to the '5' in the slice)
var last = 4 

And so we can "slice" the slice, removing undesired elements:

// keeping elements from start to 'first element to remove' (not keeping first to remove), 
// removing elements from 'first element to remove' to 'last element to remove'
// and keeping all others elements to the end of the slice
newSlice1 := append(slice[:first], slice[last+1:]...)
// > [1 2 6]

// you can do using directly numbers instead of variables
newSlice2 := append(slice[:2], slice[5:]...)
// > [1 2 6]

// Another way to do the same
newSlice3 := slice[:first + copy(slice[first:], slice[last+1:])]
// > [1 2 6]

// same that newSlice3 with hard coded indexes (without use of variables)
newSlice4 := slice[:2 + copy(slice[2:], slice[5:])]
// > [1 2 6]

To remove only one element, just have to put the index of this element as the first AND as the last index to remove, just like that:

var indexToRemove = 3
newSlice5 := append(slice[:indexToRemove], slice[indexToRemove+1:]...)
// > [1 2 3 5 6]

// hard-coded version:
newSlice5 := append(slice[:3], slice[4:]...)
// > [1 2 3 5 6]

And you can also remove elements from the beginning of the slice:

newSlice6 := append(slice[:0], slice[last+1:]...)
// > [6]

// That can be simplified into
newSlice6 := slice[last+1:]
// > [6]

You can also removing some elements from the end of the slice:

newSlice7 := append(slice[:first], slice[first+1:len(slice)-1]...)
// > [1 2]

// That can be simplified into
newSlice7 := slice[:first]
// > [1 2]

If the new slice have to contains exactly the same elements than the first one, you can use the same thing but with last := first-1.
(This can be useful in case of your indexes are previously computed)

Slices have both length and capacity. The length of a slice is the number of elements currently in the slice, while the capacity is the number of elements the slice can hold before needing to be reallocated.

When creating a slice using the built-in make() function, you can specify its length, and optionally its capacity. If the capacity is not explicitly specified, it will be the specified length.

var s = make([]int, 3, 5) // length 3, capacity 5

You can check the length of a slice with the built-in len() function:

var n = len(s) // n == 3

You can check the capacity with the built-in cap() function:

var c = cap(s) // c == 5

Elements created by make() are set to the zero value for the element type of the slice:

for idx, val := range s {
    fmt.Println(idx, val)
}
// output:
// 0 0
// 1 0
// 2 0

Run it on play.golang.org

You cannot access elements beyond the length of a slice, even if the index is within capacity:

var x = s[3] // panic: runtime error: index out of range

However, as long as the capacity exceeds the length, you can append new elements without reallocating:

var t = []int{3, 4}
s = append(s, t) // s is now []int{0, 0, 0, 3, 4}
n = len(s) // n == 5
c = cap(s) // c == 5

If you append to a slice which lacks the capacity to accept the new elements, the underlying array will be reallocated for you with sufficient capacity:

var u = []int{5, 6}
s = append(s, u) // s is now []int{0, 0, 0, 3, 4, 5, 6}
n = len(s) // n == 7
c = cap(s) // c > 5

It is, therefore, generally good practice to allocate sufficient capacity when first creating a slice, if you know how much space you'll need, to avoid unnecessary reallocations.

If you wish to copy the contents of a slice into an initially empty slice, following steps can be taken to accomplish it-

1. Create the source slice:

var sourceSlice []interface{} = []interface{}{"Hello",5.10,"World",true}

2. Create the destination slice, with:

• Length = Length of sourceSlice

var destinationSlice []interface{} = make([]interface{},len(sourceSlice))

3. Now that the destination slice's underlying array is big enough to accomodate all the elements of the source slice, we can proceed to copy the elements using the builtin copy:

copy(destinationSlice,sourceSlice)

Slices are the typical way go programmers store lists of data.

To declare a slice variable use the []Type syntax.

var a []int

To declare and initialize a slice variable in one line use the []Type{values} syntax.

var a []int = []int{3, 1, 4, 1, 5, 9}

Another way to initialize a slice is with the make function. It three arguments: the Type of the slice (or map), the length, and the capacity.

a := make([]int, 0, 5)

You can add elements to your new slice using append.

a = append(a, 5)

Check the number of elements in your slice using len.

length := len(a)

Check the capacity of your slice using cap. The capacity is the number of elements currently allocated to be in memory for the slice. You can always append to a slice at capacity as Go will automatically create a bigger slice for you.

capacity := cap(a)

You can access elements in a slice using typical indexing syntax.

a[0]  // Gets the first member of `a`

You can also use a for loop over slices with range. The first variable is the index in the specified array, and the second variable is the value for the index.

for index, value := range a {
    fmt.Println("Index: " + index + " Value: " + value)  // Prints "Index: 0 Value: 5" (and continues until end of slice)
}

Go Playground

To filter a slice without allocating a new underlying array:

// Our base slice
slice := []int{ 1, 2, 3, 4 }
// Create a zero-length slice with the same underlying array
tmp := slice[:0]

for _, v := range slice {
  if v % 2 == 0 {
    // Append desired values to slice
    tmp = append(tmp, v)
  }
}

// (Optional) Reassign the slice
slice = tmp // [2, 4]

The zero value of slice is nil, which has the length and capacity 0. A nil slice has no underlying array. But there are also non-nil slices of length and capacity 0, like []int{} or make([]int, 5)[5:].

Any type that have nil values can be converted to nil slice:

s = []int(nil)

To test whether a slice is empty, use:

if len(s) == 0　{
    fmt.Ptintf("s is empty.")
}