Is there a way to iterate over a range of integers

Question

Go s range can iterate over maps and slices  but I was wondering if there is a way to iterate over a range of numbers  something like this   for i    range  1  10        fmt Println i      Or is there a way to represent range of integers in Go like how Ruby does with the class Range

User · Answer

Here is a program to compare the two ways suggested so far

import (
    "fmt"

    "github.com/bradfitz/iter"
)

func p(i int) {
    fmt.Println(i)
}

func plain() {
    for i := 0; i < 10; i++ {
        p(i)
    }
}

func with_iter() {
    for i := range iter.N(10) {
        p(i)
    }
}

func main() {
    plain()
    with_iter()
}

Compile like this to generate disassembly

go build -gcflags -S iter.go

Here is plain (I've removed the non instructions from the listing)

setup

0035 (/home/ncw/Go/iter.go:14) MOVQ    $0,AX
0036 (/home/ncw/Go/iter.go:14) JMP     ,38

loop

0037 (/home/ncw/Go/iter.go:14) INCQ    ,AX
0038 (/home/ncw/Go/iter.go:14) CMPQ    AX,$10
0039 (/home/ncw/Go/iter.go:14) JGE     $0,45
0040 (/home/ncw/Go/iter.go:15) MOVQ    AX,i+-8(SP)
0041 (/home/ncw/Go/iter.go:15) MOVQ    AX,(SP)
0042 (/home/ncw/Go/iter.go:15) CALL    ,p+0(SB)
0043 (/home/ncw/Go/iter.go:15) MOVQ    i+-8(SP),AX
0044 (/home/ncw/Go/iter.go:14) JMP     ,37
0045 (/home/ncw/Go/iter.go:17) RET     ,

And here is with_iter

setup

0052 (/home/ncw/Go/iter.go:20) MOVQ    $10,AX
0053 (/home/ncw/Go/iter.go:20) MOVQ    $0,~r0+-24(SP)
0054 (/home/ncw/Go/iter.go:20) MOVQ    $0,~r0+-16(SP)
0055 (/home/ncw/Go/iter.go:20) MOVQ    $0,~r0+-8(SP)
0056 (/home/ncw/Go/iter.go:20) MOVQ    $type.[]struct {}+0(SB),(SP)
0057 (/home/ncw/Go/iter.go:20) MOVQ    AX,8(SP)
0058 (/home/ncw/Go/iter.go:20) MOVQ    AX,16(SP)
0059 (/home/ncw/Go/iter.go:20) PCDATA  $0,$48
0060 (/home/ncw/Go/iter.go:20) CALL    ,runtime.makeslice+0(SB)
0061 (/home/ncw/Go/iter.go:20) PCDATA  $0,$-1
0062 (/home/ncw/Go/iter.go:20) MOVQ    24(SP),DX
0063 (/home/ncw/Go/iter.go:20) MOVQ    32(SP),CX
0064 (/home/ncw/Go/iter.go:20) MOVQ    40(SP),AX
0065 (/home/ncw/Go/iter.go:20) MOVQ    DX,~r0+-24(SP)
0066 (/home/ncw/Go/iter.go:20) MOVQ    CX,~r0+-16(SP)
0067 (/home/ncw/Go/iter.go:20) MOVQ    AX,~r0+-8(SP)
0068 (/home/ncw/Go/iter.go:20) MOVQ    $0,AX
0069 (/home/ncw/Go/iter.go:20) LEAQ    ~r0+-24(SP),BX
0070 (/home/ncw/Go/iter.go:20) MOVQ    8(BX),BP
0071 (/home/ncw/Go/iter.go:20) MOVQ    BP,autotmp_0006+-32(SP)
0072 (/home/ncw/Go/iter.go:20) JMP     ,74

loop

0073 (/home/ncw/Go/iter.go:20) INCQ    ,AX
0074 (/home/ncw/Go/iter.go:20) MOVQ    autotmp_0006+-32(SP),BP
0075 (/home/ncw/Go/iter.go:20) CMPQ    AX,BP
0076 (/home/ncw/Go/iter.go:20) JGE     $0,82
0077 (/home/ncw/Go/iter.go:20) MOVQ    AX,autotmp_0005+-40(SP)
0078 (/home/ncw/Go/iter.go:21) MOVQ    AX,(SP)
0079 (/home/ncw/Go/iter.go:21) CALL    ,p+0(SB)
0080 (/home/ncw/Go/iter.go:21) MOVQ    autotmp_0005+-40(SP),AX
0081 (/home/ncw/Go/iter.go:20) JMP     ,73
0082 (/home/ncw/Go/iter.go:23) RET     ,

So you can see that the iter solution is considerably more expensive even though it is fully inlined in the setup phase. In the loop phase there is an extra instruction in the loop, but it isn't too bad.

I'd use the simple for loop.

User · Answer

Here s a benchmark to compare a Go for statement with a ForClause and a Go range statement using the iter package   iter test go  package main  import        testing        github com bradfitz iter     const loops   1e6  func BenchmarkForClause b  testing B        b ReportAllocs       j    0     for i    0  i  lt  b N  i             for j   0  j  lt  loops  j                 j   j                         j    func BenchmarkRangeIter b  testing B        b ReportAllocs       j    0     for i    0  i  lt  b N  i             for j   range iter N loops                j   j                         j       It does not cause any allocations  func N n int    struct         return make   struct    n     func BenchmarkIterAllocs b  testing B        b ReportAllocs       var n   struct       for i    0  i  lt  b N  i             n   iter N loops                n     Output     go test -bench   -run   testing  warning  no tests to run PASS BenchmarkForClause      2000       1260356 ns op           0 B op          0 allocs op BenchmarkRangeIter      2000       1257312 ns op           0 B op          0 allocs op BenchmarkIterAllocs 20000000            82 2 ns op         0 B op          0 allocs op ok      so test 7 026s

User · Answer

If you want to just iterate over a range w o using and indices or anything else  this code sample worked just fine for me  No extra declaration needed  no    Haven t checked the performance  though   for range  N int            Body        P S  The very first day in GoLang  Please  do critique if it s a wrong approach

User · Answer

You can  and should  just write a for loop  Simple  obvious code is the Go way   for i    1  i  lt   10  i         fmt Println i

User · Answer

It was suggested by Mark Mishyn to use slice but there is no reason to create array with make and use in for returned slice of it when array created via literal can be used and it s shorter  for i    range  5 int             fmt Println i

User · Answer

The problem is not the range  the problem is how the end of slice is calculated  with a fixed number 10 the simple for loop is ok but with a calculated size like bfl Size   you get a function-call on every iteration  A simple range over int32 would help because this evaluate the bfl Size   only once  type BFLT PerfServer      func  this  BFLT  Call         bfl    MqBufferLCreateTLS 0                                                                                         for this ReadItemExists                                                                                               bfl AppendU this ReadU                                                                                                  this SendSTART          size    bfl Size        for i    int32 0   i  lt  bfl Size      size     i                                                                                        this SendU bfl IndexGet i                                                                                               this SendRETURN

User · Answer

Here is a compact  dynamic version that doesn t depend on iter  but works similarly   package main  import        quot fmt quot        N is an alias for an unallocated struct func N size int    struct         return make   struct    size     func main         size    1000     for i    range N size            fmt Println i            With some tweaks size could be of type uint64  if needed  but that s the gist

User · Answer

iter is a very small package that just provides a syntantically different way to iterate over integers   for i    range iter N 4        fmt Println i      Rob Pike  an author of Go  has criticized it      It seems that almost every time someone comes up with a way to avoid    doing something like a for loop the idiomatic way  because it feels    too long or cumbersome  the result is almost always more keystrokes    than the thing that is supposedly shorter        That s leaving aside all the crazy overhead these  improvements  bring

User · Answer

package main  import  fmt   func main          nums      int 2  3  4      for    num    range nums          fmt Println num  sum

User · Answer

While I commiserate with your concern about lacking this language feature  you re probably just going to want to use a normal for loop  And you ll probably be more okay with that than you think as you write more Go code   I wrote this iter package     which is backed by a simple  idiomatic for loop that returns values over a chan int     in an attempt to improve on the design found in https   github com bradfitz iter  which has been pointed out to have caching and performance issues  as well as a clever  but strange and unintuitive implementation  My own version operates the same way   package main  import        fmt       github com drgrib iter     func main         for i    range iter N 10            fmt Println i            However  benchmarking revealed that the use of a channel was a very expensive option  The comparison of the 3 methods  which can be run from iter test go in my package using  go test -bench   -run     quantifies just how poor its performance is  BenchmarkForMany-4                   5000       329956 ns op           0 B op          0 allocs op BenchmarkDrgribIterMany-4               5    229904527 ns op         195 B op          1 allocs op BenchmarkBradfitzIterMany-4          5000       337952 ns op           0 B op          0 allocs op  BenchmarkFor10-4                500000000         3 27 ns op           0 B op          0 allocs op BenchmarkDrgribIter10-4            500000      2907 ns op             96 B op          1 allocs op BenchmarkBradfitzIter10-4       100000000        12 1 ns op            0 B op          0 allocs op   In the process  this benchmark also shows how the bradfitz solution underperforms in comparison to the built-in for clause for a loop size of 10   In short  there appears to be no way discovered so far to duplicate the performance of the built-in for clause while providing a simple syntax for  0 n  like the one found in Python and Ruby   Which is a shame because it would probably be easy for the Go team to add a simple rule to the compiler to change a line like  for i    range 10       fmt Println i      to the same machine code as for i    0  i  lt  10  i     However  to be fair  after writing my own iter N  but before benchmarking it   I went back through a recently written program to see all the places I could use it  There actually weren t many  There was only one spot  in a non-vital section of my code  where I could get by without the more complete  default for clause   So while it may look like this is a huge disappointment for the language in principle  you may find     like I did     that you actually don t really need it in practice  Like Rob Pike is known to say for generics  you might not actually miss this feature as much as you think you will

User · Answer

You can also check out github com wushilin stream  It is a lazy stream like concept of java util stream      It doesn t really allocate the 10 elements  stream1    stream Range 0  10      Print each element  stream1 Each print      Add 3 to each element  but it is a lazy add     You only add when consume the stream stream2    stream1 Map func i int  int       return i   3        Well  this consumes the stream   gt  return sum of stream2  stream2 Reduce func i  j int  int       return i   j        Create stream with 5 elements stream3    stream Of 1  2  3  4  5      Create stream from array stream4    stream FromArray arrayInput      Filter stream3  keep only elements that is bigger than 2     and return the Sum  which is 12 stream3 Filter func i int  bool       return i  gt  2    Sum     Hope this helps

User · Answer

I have written a package in Golang which mimic the Python s range function   Package https   github com thedevsaddam iter  package main  import        fmt        github com thedevsaddam iter     func main            sequence  0-9     for v    range iter N 10            fmt Printf   d    v            fmt Println          output  0 1 2 3 4 5 6 7 8 9         sequence  5-9     for v    range iter N 5  10            fmt Printf   d    v            fmt Println          output  5 6 7 8 9         sequence  1-9  increment by 2     for v    range iter N 5  10  2            fmt Printf   d    v            fmt Println          output  5 7 9         sequence  a-e     for v    range iter L  a    e             fmt Printf   s    string v             fmt Println          output  a b c d e         Note  I have written for fun  Btw  sometimes it may be helpful

[go] Is there a way to iterate over a range of integers?

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