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do not create wait groups for slices with len less than 2 #517

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do not create wait groups for slices with len less than 2 #517

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45 changes: 44 additions & 1 deletion parallel/slice.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,14 @@ import "sync"
// Map manipulates a slice and transforms it to a slice of another type.
// `iteratee` is call in parallel. Result keep the same order.
func Map[T any, R any](collection []T, iteratee func(item T, index int) R) []R {
if len(collection) == 0 {
return []R{}
}

if len(collection) == 1 {
return []R{iteratee(collection[0], 0)}
}

result := make([]R, len(collection))

var wg sync.WaitGroup
Expand All @@ -28,6 +36,15 @@ func Map[T any, R any](collection []T, iteratee func(item T, index int) R) []R {
// ForEach iterates over elements of collection and invokes iteratee for each element.
// `iteratee` is call in parallel.
func ForEach[T any](collection []T, iteratee func(item T, index int)) {
if len(collection) == 0 {
return
}

if len(collection) == 1 {
iteratee(collection[0], 0)
return
}

var wg sync.WaitGroup
wg.Add(len(collection))

Expand All @@ -45,6 +62,14 @@ func ForEach[T any](collection []T, iteratee func(item T, index int)) {
// The iteratee is invoked with index as argument.
// `iteratee` is call in parallel.
func Times[T any](count int, iteratee func(index int) T) []T {
if count == 0 {
return []T{}
}

if count == 1 {
return []T{iteratee(0)}
}

result := make([]T, count)

var wg sync.WaitGroup
Expand All @@ -70,6 +95,16 @@ func Times[T any](count int, iteratee func(index int) T) []T {
func GroupBy[T any, U comparable, Slice ~[]T](collection Slice, iteratee func(item T) U) map[U]Slice {
result := map[U]Slice{}

if len(collection) == 0 {
return result
}

if len(collection) == 1 {
key := iteratee(collection[0])
result[key] = collection
return result
}

var mu sync.Mutex
var wg sync.WaitGroup
wg.Add(len(collection))
Expand Down Expand Up @@ -97,7 +132,15 @@ func GroupBy[T any, U comparable, Slice ~[]T](collection Slice, iteratee func(it
// of running each element of collection through iteratee.
// `iteratee` is call in parallel.
func PartitionBy[T any, K comparable, Slice ~[]T](collection Slice, iteratee func(item T) K) []Slice {
result := []Slice{}
if len(collection) == 0 {
return []Slice{}
}

if len(collection) == 1 {
return []Slice{collection}
}

result := make([]Slice, 0, 1)
seen := map[K]int{}

var mu sync.Mutex
Expand Down