lean into examples

examples/sorting-by-functions/sorting-by-functions.go

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+// Sometimes we'll want to sort a collection by something
+// other than its natural order. For example, suppose we
+// wanted to sort strings by their length instead of
+// alphabetically. Here's an example of custom sorts sorts
+// in Go.
+
+package main
+
+import "sort"
+import "fmt"
+
+// In order to sort by a custom function in Go, we need a
+// corresponding type. Here we've created a `ByLength`
+// type that is just an alias for the builtin `[]string`
+// type.
+type ByLength []string
+
+// We implement `sort.Interface` - `Len`, `Less`, and
+// `Swap` - on our type so we can use the `sort` package's
+// generic `Sort` function. `Len` and `Swap`
+// will usually be similar accross types and `Less` will
+// hold the actual custom sorting logic. In our case we
+// want to sort in order of increasing string length, so
+// we use `len(s[i])` and `len(s[j])` here.
+func (s ByLength) Len() int {
+    return len(s)
+}
+func (s ByLength) Swap(i, j int) {
+    s[i], s[j] = s[j], s[i]
+}
+func (s ByLength) Less(i, j int) bool {
+    return len(s[i]) < len(s[j])
+}
+
+// With all of this in place, we can now implement our
+// custom sort by casting the original `fruits` slice to
+// `ByLength`, and then use `sort.Sort` on that typed
+// slice.
+func main() {
+    fruits := []string{"peach", "banana", "kiwi"}
+    sort.Sort(ByLength(fruits))
+    fmt.Println(fruits)
+}