一种在Go中对结构片段进行排序的灵活而优雅的方法[关闭]
Let us say that we have a fairly complicated struct with numerous fields, that I need to sort in several places according to different criteria, e.g.
type MySuperType struct {
x0, x1, x2, x3 xType
// possibly even more fields
}
// sort 1: ascending x0, then descending x1, then more stuff
// sort 2: if x4==0 then applyCriteria2a else applyCriteria2b
func f1(mySuperSlice []MySuperType) {
// sort 'myList' according sort #1
// do something with the sorted list
}
func f2(mySuperSlice []MySuperType) {
// sort 'myList' according sort #2
// do something with the sorted list
}
func f3(mySuperSlice []MySuperType) {
// sort 'myList' according sort #1, note: we use sort #1 again!
// do something with the sorted list
}
Proposed solution 1:
Create a new type (alias of []MySuperType) that implements sort.Interface for each sorting criteria required.
Problems:
(i) there is some duplicated code, as the functions Len and Swap are going to be identical
(ii) there is going to be a bunch of new types lying around that do not help with the overall readability of the program --- these new types don't really represent anything, plus the only thing that really matters is the Less function.
Proposed solution 2:
Use sort.Slice
It would be the perfect solution (see this answer), but from my understanding, the sorting function has to be specified inline (I get an error invalid receiver type []T ([]T is an unnamed type) when I tried to define it elsewhere, which means that I need to define an alias for []T and we are back to solution 1).
Now, the problem with defining the function inline is that (i) given the complexity of MySuperType, the function can be very long and (ii) the functions are going to be duplicated in several place (e.g. in f1 and f3 in my example above) -- much more annoying that in solution 1 as the sorting functions can be long and complex.
Note: (i) would not be that much of an issue if we did not have (ii) actually
Question:
Given my current understanding and knowledge of Go, I would use solution 1.
But does anyone knows a different approach that elegantly solves this problem or suggestions to improve the drawbacks listed above?
@ThunderCat's solution will work. Another option would be to write functions that return closures over the slice that match the signature for the less argument of sort.Slice:
func ascX0DescX1(s []MySuperType) (func(int, int) bool) {
return func(i, j int) bool {
if s[i].x0 == s[j].x0 {
return s[i].x1 > s[j].x1
}
return s[i].x0 < s[j].x0
}
}
Then pass that as the less arg to sort.Slice:
sort.Slice(mySuperSlice, ascX0DescX1(mySuperSlice))
Write sort a sort function for each ordering and call from f1, f2 and f3 as appropriate:
func sortByX0AscX1Desc(s []MySuperType) {
sort.Slice(s, func(i, j int) bool {
switch {
case s[i].x0 < s[j].x0:
return true
case s[i].x0 > s[j].x0:
return false
case s[i].x1 > s[j].x1:
return true
default:
return false
}
})
}
func f1(mySuperSlice []MySuperType) {
sortByX0AscX1Desc(mySuperSlice)
// do something with the sorted list
}
func f2(mySuperSlice []MySuperType) {
sortBySomethingElse(mySuperSlice)
// do something with the sorted list
}
func f3(mySuperSlice []MySuperType) {
sortByX0AscX1Desc(mySuperSlice)
// do something with the sorted list
}
You could also omit the extra function and call sort where you need it.
type MySuperType struct {
x0, x1, x2, x3 string
}
func f1() {
fields := []MySuperType {
{ "a1", "b4", "c3", "d2" },
{ "a2", "b1", "c2", "d3" },
{ "a3", "b1", "c4", "d1" },
{ "a4", "b3", "c1", "d4" },
}
sort.SliceStable(fields, func(i, j int) bool {
return fields[i].x1 < fields[j].x1 || fields[i].x2 > fields[j].x2
})
fmt.Println("by x1, then x2: ", fields)
}
Result: by x1, then x2: [{a3 b1 c4 d1} {a2 b1 c2 d3} {a4 b3 c1 d4} {a1 b4 c3 d2}]