2023-01-04

chapter-3-composite-types/02_slices.go

@@ -6,6 +6,8 @@ package main
 
 import "fmt"
 
+func UNUSED(x ...interface{}) {}
+
 func main() {
 	// []int makes a slice, [...]int makes an array
 	x := []int{10, 20, 30}
@@ -59,9 +61,11 @@ func main() {
 	z = append(z, 40)
 	fmt.Println(z, len(z), cap(z))
 	z = append(z, 50)
+
 	fmt.Println(z, len(z), cap(z))
 	fmt.Println()
 
+	//
 	// make specifies type, length, capacity
 
 	// slice of ints length 5 (5 0's)
@@ -77,4 +81,48 @@ func main() {
 	b = append(b, 1)
 	fmt.Println(b, len(b), cap(b))
 	fmt.Println()
+
+	//
+	// Declaring slices
+	// the idea is to minimise the number of times it needs to grow
+
+	// slice that is nil (use when it might stay null)
+	var data_nil []int
+	UNUSED(data_nil)
+
+	// slice that is empty (not nill)
+	var data_empty = []int{}
+	UNUSED(data_empty)
+
+	// slice literal
+	// useful if you have starting values/values that won't change (hardcoded)
+	data_literal := []int{1, 2, 3}
+	UNUSED(data_literal)
+
+	// slice make
+	// if you have an idea how large the slice should be, but not the values, use `make`
+
+	// option 1 - specify non-zero length - useful for using slices as buffers
+	data_option_1 := make([]int, 5)
+	UNUSED(data_option_1)
+
+	// option 2 - specify exact length - if you know the exact length you nneed
+	data_option_2 := make([]int, 10)
+	UNUSED(data_option_2)
+
+	// option 3 - zero length & capacity - for everything else
+	data_option_3 := make([]int, 0, 10)
+	UNUSED(data_option_3)
+
+	//
+	// Slicing slices
+	sliced := []int{1, 2, 3, 4, 5}
+	sliced_first_2 := sliced[:2]
+	sliced_skip_first := sliced[1:]
+	sliced_middle := sliced[2:3]
+	fmt.Println("slicing slices")
+	fmt.Println("slice:", sliced)
+	fmt.Println("sliced_first_2:", sliced_first_2)
+	fmt.Println("sliced_skip_first:", sliced_skip_first)
+	fmt.Println("sliced_middle:", sliced_middle)
 }