Go has new generic slices and map packages

Since the introduction of generics in Go 1.18, there have been discussions about adding new helper functions to the standard library to cover most frequent operations. After more than a year, two new libraries with generics will be added¹² into the Go standard library starting from Go 1.21.

You can already find them here: https://pkg.go.dev/golang.org/x/exp/slices https://pkg.go.dev/golang.org/x/exp/maps

Or install via:

go get golang.org/x/exp

Examples

Here are some examples of how you can improve your codebase with the new slices library.

Copy a slice

// Before
a := []int{1, 2, 3}  
b := make([]int, len(a))  
copy(b, a)

// after
a := []int{1, 2, 3}  
b := slices.Clone(a)

Check slice contains value

// Before
a := []int{1, 2, 3}  
toFind := 2  
for _, v := range a {  
   if v == toFind {  
      fmt.Printf("slice 'a' contains %v", toFind), 2)  
      break
   }
}

// After
a := []int{1, 2, 3}  
toFind := 2  
if slices.Contains(a, toFind) {  
   fmt.Printf("slice 'a' contains %v", toFind), 2)  
}

Insert into slice

// Before
a := []int{1, 2, 3}  
val, insertIdx := 4, 1  
// disclaimer: not the best way to insert into a slice  
b := append(a[:insertIdx], append([]int{val}, a[insertIdx:]...)...) // [1 4 2 3]

// After
a := []int{1, 2, 3}  
val, insertIdx := 4, 1  
b := slices.Insert(a, insertIdx, val)

Check slices are equal

// Before
a := []int{1, 2, 3}  
b := []int{1, 2, 3}  
  
areEqual := true  
for i, _ := range a {  
   if a[i] != b[i] {  
      areEqual = false  
      break
    }  
}
fmt.Print(areEqual) // true

// After
a := []int{1, 2, 3}  
b := []int{1, 2, 3}  
areEqual := slices.Equal(a, b)
fmt.Print(areEqual) // true

Grow slice

// Before
a := []int{1}  
n := 5  
a = append(a[:cap(a)], make([]int, n)...)[:len(a)]
fmt.Printf("slice cap: %v", cap(a)) // 6
fmt.Printf("slice len: %v", len(a) //  1

// After
a := slices.Grow([]int{1}, 5)  
fmt.Printf("slice cap: %v", cap(a)) // 6
fmt.Printf("slice len: %v", len(a) //  1