Suggest Go 1.8 sort.Slice

[bradleyfalzon]

Pre 1.8 to sort a slice of person by age:

package main

import (
        "fmt"
        "sort"
)

type Person struct {
        Name string
        Age  int
}

type ByAge []Person

func (a ByAge) Len() int           { return len(a) }
func (a ByAge) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
func (a ByAge) Less(i, j int) bool { return a[i].Age < a[j].Age }

func main() {
        people := []Person{
                {"Bob", 31},
                {"John", 42},
                {"Michael", 17},
                {"Jenny", 26},
        }

        fmt.Println(people)
        sort.Sort(ByAge(people))
        fmt.Println(people)
}

Post 1.8 using https://tip.golang.org/pkg/sort/#Slice

package main

import (
        "fmt"
        "sort"
)

type Person struct {
        Name string
        Age  int
}

func main() {
        people := []Person{
                {"Bob", 31},
                {"John", 42},
                {"Michael", 17},
                {"Jenny", 26},
        }

        fmt.Println(people)
        sort.Slice(people, func(i, j int) bool { return people[i].Age < people[j].Age })
        fmt.Println(people)
}

[bradleyfalzon]

Go 1.8 adds the following slice helpers to the sort package

Slice(slice interface{}, less func(i, j int) bool)
SliceIsSorted(slice interface{}, less func(i, j int) bool) bool
SliceStable(slice interface{}, less func(i, j int) bool)

It appears we could just check for calls to sort.Slice{,Stable,IsSorted} with a slice (taking into account a possible cast to something that implements sort.Interface). If it's a slice, we can suggest a simplification to sort.Slice{,Stable,IsSorted}.

I can't imagine any conceivable reasons someone may want to ignore the suggestion, as I can't imagine anyone implementing the Len or Swap methods any differently.

Would it be safe to implement this check, and if a maintainer wants to support pre Go 1.8, they can use the ignore flags?

If no-one has any immediate concerns/suggestions/alternatives, I may attempt to implement this check myself soon.

[dominikh]

@bradleyfalzon Please leave implementing the check to me, I already made some mental notes regarding its implementation.