Awesome

iter

Note: I'm currently working on making it work with Go generics. For previous version, please check v1 branch.

Go implementation of C++ STL iterators and algorithms.

Less hand-written loops, more expressive code.

README translations: 简体中文

Motivation

Although Go doesn't have generics, we deserve to have reuseable general algorithms. iter helps improving Go code in several ways:

Some simple loops are unlikely to be wrong or inefficient, but calling algorithm instead will make the code more concise and easier to comprehend. Such as AllOf, FindIf, Accumulate.
Some algorithms are not complicated, but it is not easy to write them correctly. Reusing code makes them easier to reason for correctness. Such as Shuffle, Sample, Partition.
STL also includes some complicated algorithms that may take hours to make it correct. Implementing it manually is impractical. Such as NthElement, StablePartition, NextPermutation.
The implementation in the library contains some imperceptible performance optimizations. For instance, MinmaxElement is done by taking two elements at a time. In this way, the overall number of comparisons is significantly reduced.

There are alternative libraries have similar goals, such as gostl, gods and go-stp. What makes iter unique is:

Non-intrusive. Instead of introducing new containers, iter tends to reuse existed containers in Go (slice, string, list.List, etc.) and use iterators to adapt them to algorithms.
Full algorithms (>100). It includes almost all algorithms come before C++17. Check the Full List.

Examples

The examples are run with some function alias to make it simple. See example_test.go for the detail.

<table> <thead><tr><th colspan="2">Print a list.List</th></tr></thead> <tbody><td>

l := list.New()
for i := 1; i <= 5; i++ {
  l.PushBack(i)
}
for e := l.Front(); e != nil; e = e.Next() {
  fmt.Print(e.Value)
  if e.Next() != nil {
    fmt.Print("->")
  }
}
// Output:
// 1->2->3->4->5

</td><td>

l := list.New()
GenerateN(ListBackInserter(l), 5, IotaGenerator(1))
Copy(lBegin(l), lEnd(l), IOWriter(os.Stdout, "->"))
// Output:
// 1->2->3->4->5

</td></tr></tbody> <thead><tr><th colspan="2">Reverse a string</th></tr></thead> <tbody><tr><td>

s := "!dlrow olleH"
var sb strings.Builder
for i := len(s) - 1; i >= 0; i-- {
  sb.WriteByte(s[i])
}
fmt.Println(sb.String())

b := []byte(s)
for i := len(s)/2 - 1; i >= 0; i-- {
  j := len(s) - 1 - i
  b[i], b[j] = b[j], b[i]
}
fmt.Println(string(b))
// Output:
// Hello world!
// Hello world!

</td><td>

s := "!dlrow olleH"
fmt.Println(MakeString(StringRBegin(s), StringREnd(s)))

b := []byte(s)
Reverse(begin(b), end(b))
fmt.Println(string(b))
// Output:
// Hello world!
// Hello world!

</td></tr></tbody> <thead><tr><th colspan="2">In-place deduplicate (from <a href="https://github.com/golang/go/wiki/SliceTricks#in-place-deduplicate-comparable">SliceTricks</a>, with minor change)</th></tr></thead> <tbody><tr><td>

in := []int{3, 2, 1, 4, 3, 2, 1, 4, 1}
sort.Ints(in)
j := 0
for i := 1; i < len(in); i++ {
  if in[j] == in[i] {
    continue
  }
  j++
  in[j] = in[i]
}
in = in[:j+1]
fmt.Println(in)
// Output:
// [1 2 3 4]

</td><td>

in := []int{3, 2, 1, 4, 3, 2, 1, 4, 1}
Sort(begin(in), end(in))
Erase(&in, Unique(begin(in), end(in)))
fmt.Println(in)
// Output:
// [1 2 3 4]

</td></tr></tbody> <thead><tr><th colspan="2">Sum all integers received from a channel</th></tr></thead> <tbody><tr><td>

ch := make(chan int)
go func() {
  for _, x := range rand.Perm(100) {
    ch <- x + 1
  }
  close(ch)
}()
var sum int
for x := range ch {
  sum += x
}
fmt.Println(sum)
// Output:
// 5050

</td><td>

ch := make(chan int)
go func() {
  CopyN(IotaReader(1), 100, ChanWriter(ch))
  close(ch)
}()
fmt.Println(Accumulate(ChanReader(ch), ChanEOF, 0))
// Output:
// 5050

</td></tr></tbody> <thead><tr><th colspan="2">Remove consecutive spaces in a string</th></tr></thead> <tbody><tr><td>

str := "  a  quick   brown  fox  "
var sb strings.Builder
var prevIsSpace bool
for i := 0; i < len(str); i++ {
  if str[i] != ' ' || !prevIsSpace {
    sb.WriteByte(str[i])
  }
  prevIsSpace = str[i] == ' '
}
fmt.Println(sb.String())
// Output:
// a quick brown fox

</td><td>

str := "  a  quick   brown  fox  "
var sb StringBuilderInserter
UniqueCopyIf(sBegin(str), sEnd(str), &sb,
  func(x, y Any) bool { return x.(byte) == ' ' && y.(byte) == ' ' })
fmt.Println(sb.String())
// Output:
// a quick brown fox

</td></tr></tbody> <thead><tr><th colspan="2">Collect N maximum elements from a channel</th></tr></thead> <tbody><tr><td>

// Need to manually mantain a min-heap.

</td><td>

top := make([]int, 5)
PartialSortCopyBy(ChanReader(ch), ChanEOF, begin(top), end(top),
  func(x, y Any) bool { return x.(int) > y.(int) })
Copy(begin(top), end(top), IOWriter(os.Stdout, ", "))

</td></tr></tbody> <thead><tr><th colspan="2">Print all permutations of ["a", "b", "c"]</th></tr></thead> <tbody><tr><td>

// Usually requires some sort of recursion

</td><td>

s := []string{"a", "b", "c"}
for ok := true; ok; ok = NextPermutation(begin(s), end(s)) {
  fmt.Println(s)
}
// Output:
// [a b c]
// [a c b]
// [b a c]
// [b c a]
// [c a b]
// [c b a]

</td></tr></tbody> </table>

Thanks

License

BSD 3-Clause