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  • Equivalent of #map in ruby in golang

    - by Oct
    I'm playing with Go and run into something I'm unable to find in Google, although there is certainly something that exists: I'm using the following struct: type Syntax struct { name string extensions *regexp.Regexp } type Scanner struct { classifier * bayesian.Classifier save_file string name_to_syntax map[string] *Syntax extensions_to_syntax map[*regexp.Regexp] *Syntax } I'd like to perform the following using Go and I'm quoting ruby because it's how I'd do that using ruby: test_regexpes = my_scanner.extensions_to_syntax.keys My goal is to get an array of *regexp.Regexp . Any idea on how to do that in a simple way ? Thank you !

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  • golang closure variable scope

    - by waaadim
    I'm reading 'CreateSpace An Introduction to Programming in Go 2012' and on page 86 I found this evil magic func makeEvenGenerator() func() uint { i := uint(0) return func() (ret uint) { ret = i i += 2 return } } // here's how it's called nextEven := makeEvenGenerator() fmt.Println(nextEven()) fmt.Println(nextEven()) fmt.Println(nextEven()) 1) Why is i not resetting ? 2) is nextEven() returning and uint or is Println so smart that it can work with everything ?

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  • Defining golang struct function using pointer or not

    - by Jacob
    Can someone explain to me why appending to an array works when you do this: func (s *Sample) Append(name string) { d := &Stuff{ name: name, } s.data = append(s.data, d) } Full code here But not when you do this: func (s Sample) Append(name string) { d := &Stuff{ name: name, } s.data = append(s.data, d) } Is there any reason at all why you would want to use the second example.

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  • golang dynamically parsing files

    - by Brian Voelker
    For parsing files i have setup a variable for template.ParseFiles and i currently have to manually set each file. Two things: How would i be able to walk through a main folder and a multitude of subfolders and automatically add them to ParseFiles so i dont have to manually add each file individually? How would i be able to call a file with the same name in a subfolder because currently I get an error at runtime if i add same name file in ParseFiles. var templates = template.Must(template.ParseFiles( "index.html", // main file "subfolder/index.html" // subfolder with same filename errors on runtime "includes/header.html", "includes/footer.html", )) func main() { // Walk and ParseFiles filepath.Walk("files", func(path string, info os.FileInfo, err error) { if !info.IsDir() { // Add path to ParseFiles } return }) http.HandleFunc("/", home) http.ListenAndServe(":8080", nil) } func home(w http.ResponseWriter, r *http.Request) { render(w, "index.html") } func render(w http.ResponseWriter, tmpl string) { err := templates.ExecuteTemplate(w, tmpl, nil) if err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) } }

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  • Writing a Python extension in Go (golang)

    - by tehwalrus
    I currently use Cython to link C and Python, and get speedup in slow bits of python code. However, I'd like to use go routines to implement a really slow (and very parallelizable) bit of code, but it must be callable from python. (I've already seen this question) I'm (sort of) happy to go via C (or Cython) to set up data structures etc if necessary, but avoiding this extra layer would be good from a bug fix/avoidance point of view. What is the simplest way to do this without having to reinvent any wheels?

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  • Go XML Unmarshal example doesn't compile

    - by marketer
    The Xml example in the go docs is broken. Does anyone know how to make it work? When I compile it, the result is: xmlexample.go:34: cannot use "name" (type string) as type xml.Name in field value xmlexample.go:34: cannot use nil as type string in field value xmlexample.go:34: too few values in struct initializer Here is the relevant code: package main import ( "bytes" "xml" ) type Email struct { Where string "attr"; Addr string; } type Result struct { XMLName xml.Name "result"; Name string; Phone string; Email []Email; } var buf = bytes.NewBufferString ( ` <result> <email where="home"> <addr>[email protected]</addr> </email> <email where='work'> <addr>[email protected]</addr> </email> <name>Grace R. Emlin</name> <address>123 Main Street</address> </result>`) func main() { var result = Result{ "name", "phone", nil } xml.Unmarshal ( buf , &result ) println ( result.Name ) }

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  • How to have a function with a nullable string parameter in Go?

    - by yuku
    I'm used to Java's String where we can pass null rather than "" for special meanings, such as use a default value. In Go, string is a primitive type, so I cannot pass nil (null) to a parameter that requires a string. I could write the function using pointer type, like this: func f(s *string) so caller can call that function either as f(nil) or // not so elegant temp := "hello"; f(&temp) but the following is unfortunately not allowed: // elegant but disallowed f(&"hello"); What is the best way to have a parameter that receives either a string or nil?

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  • Go: using a pointer to array

    - by Sean
    I'm having a little play with google's Go language, and I've run into something which is fairly basic in C but doesn't seem to be covered in the documentation I've seen so far When I pass a pointer to an array to a function, I presumed we'd have some way to access it as follows: func conv(x []int, xlen int, h []int, hlen int, y *[]int) for i := 0; i<xlen; i++ { for j := 0; j<hlen; j++ { *y[i+j] += x[i]*h[j] } } } But the Go compiler doesn't like this: sean@spray:~/dev$ 8g broke.go broke.go:8: invalid operation: y[i + j] (index of type *[]int) Fair enough - it was just a guess. I have got a fairly straightforward workaround: func conv(x []int, xlen int, h []int, hlen int, y_ *[]int) { y := *y_ for i := 0; i<xlen; i++ { for j := 0; j<hlen; j++ { y[i+j] += x[i]*h[j] } } } But surely there's a better way. The annoying thing is that googling for info on Go isn't very useful as all sorts of C\C++\unrelated results appear for most search terms.

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  • With Go, how to append unknown number of byte into a vector and get a slice of bytes?

    - by Stephen Hsu
    I'm trying to encode a large number to a list of bytes(uint8 in Go). The number of bytes is unknown, so I'd like to use vector. But Go doesn't provide vector of byte, what can I do? And is it possible to get a slice of such a byte vector? I intends to implement data compression. Instead of store small and large number with the same number of bytes, I'm implements a variable bytes that uses less bytes with small number and more bytes with large number. My code can not compile, invalid type assertion: 1 package main 2 3 import ( 4 //"fmt" 5 "container/vector" 6 ) 7 8 func vbEncodeNumber(n uint) []byte{ 9 bytes := new(vector.Vector) 10 for { 11 bytes.Push(n % 128) 12 if n < 128 { 13 break 14 } 15 n /= 128 16 } 17 bytes.Set(bytes.Len()-1, bytes.Last().(byte)+byte(128)) 18 return bytes.Data().([]byte) // <- 19 } 20 21 func main() { vbEncodeNumber(10000) } I wish to writes a lot of such code into binary file, so I wish the func can return byte array. I haven't find a code example on vector.

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  • Is there a version of the removeElement function in Go for the vector package like Java has in its V

    - by Brian T Hannan
    I am porting over some Java code into Google's Go language and I converting all code except I am stuck on just one part after an amazingly smooth port. My Go code looks like this and the section I am talking about is commented out: func main() { var puzzleHistory * vector.Vector; puzzleHistory = vector.New(0); var puzzle PegPuzzle; puzzle.InitPegPuzzle(3,2); puzzleHistory.Push(puzzle); var copyPuzzle PegPuzzle; var currentPuzzle PegPuzzle; currentPuzzle = puzzleHistory.At(0).(PegPuzzle); isDone := false; for !isDone { currentPuzzle = puzzleHistory.At(0).(PegPuzzle); currentPuzzle.findAllValidMoves(); for i := 0; i < currentPuzzle.validMoves.Len(); i++ { copyPuzzle.NewPegPuzzle(currentPuzzle.holes, currentPuzzle.movesAlreadyDone); copyPuzzle.doMove(currentPuzzle.validMoves.At(i).(Move)); // There is no function in Go's Vector that will remove an element like Java's Vector //puzzleHistory.removeElement(currentPuzzle); copyPuzzle.findAllValidMoves(); if copyPuzzle.validMoves.Len() != 0 { puzzleHistory.Push(copyPuzzle); } if copyPuzzle.isSolutionPuzzle() { fmt.Printf("Puzzle Solved"); copyPuzzle.show(); isDone = true; } } } } If there is no version available, which I believe there isn't ... does anyone know how I would go about implementing such a thing on my own?

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  • Are vector assignments copied by value or by reference in Google's Go language?

    - by Brian T Hannan
    In the following code, I create one peg puzzle then do a move on it which adds a move to its movesAlreadyDone vector. Then I create another peg puzzle then do a move on it which adds a move to its movesAlreadyDone vector. When I print out the values in that vector for the second one, it has the move in it from the first one along with the move from the second one. Can anyone tell me why it seems to be assigning by reference and not value? Are vector assignments copied by value or by reference in Google's Go language? package main import "fmt" import "container/vector" type Move struct { x0, y0, x1, y1 int } type PegPuzzle struct { movesAlreadyDone * vector.Vector; } func (p *PegPuzzle) InitPegPuzzle(){ p.movesAlreadyDone = vector.New(0); } func NewChildPegPuzzle(parent *PegPuzzle) *PegPuzzle{ retVal := new(PegPuzzle); retVal.movesAlreadyDone = parent.movesAlreadyDone; return retVal } func (p *PegPuzzle) doMove(move Move){ p.movesAlreadyDone.Push(move); } func (p *PegPuzzle) printPuzzleInfo(){ fmt.Printf("-----------START----------------------\n"); fmt.Printf("moves already done: %v\n", p.movesAlreadyDone); fmt.Printf("------------END-----------------------\n"); } func main() { p := new(PegPuzzle); cp1 := new(PegPuzzle); cp2 := new(PegPuzzle); p.InitPegPuzzle(); cp1 = NewChildPegPuzzle(p); cp1.doMove(Move{1,1,2,3}); cp1.printPuzzleInfo(); cp2 = NewChildPegPuzzle(p); cp2.doMove(Move{3,2,5,1}); cp2.printPuzzleInfo(); } Any help will be greatly appreciated. Thanks!

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  • How do I put a vector inside of a struct in Go?

    - by Brian T Hannan
    I'm trying to put a vector variable inside a struct in Google's Go programming language. This is what I have so far: Want: type Point struct { x, y int } type myStruct struct { myVectorInsideStruct vector; } func main(){ myMyStruct := myStruct{vector.New(0)}; myPoint := Point{2,3}; myMyStruct.myVectorInsideStruct.Push(myPoint); } Have: type Point struct { x, y int } func main(){ myVector := vector.New(0); myPoint := Point{2,3}; myVector.Push(myPoint); } I can get the vector to work in my main function just fine, but I want to encapsulate it inside a struct for easier use.

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  • To use package properly, how to arrange directory, file name, unit test file?

    - by Stephen Hsu
    My source files tree is like this: /src /pkg /foo foo.go foo_test.go Inside foo.go: package foo func bar(n int) { ... } inside foo_test.go: package foo func testBar(t *testing.T) { bar(10) ... } My questions are: Does package name relates to directory name, source file name? If there is only one source file for a package, need I put it in a directory? Should I put foo.go and foo_test.go in the same package? In the foo_test.go, as it's in the same package as foo.go, I didn't import foo. But when I compile foo_test.go with 6g, it says bar() is undefined. What should I do?

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  • What is the difference between panic and an assert?

    - by acidzombie24
    Go doesn't provide assertions. They are undeniably convenient, but our experience has been that programmers use them as a crutch to avoid thinking about proper error handling and reporting. However it has print and println which does panic like print, aborts execution after printing panicln like println, aborts execution after printing Isnt that the same thing as an assert? Why would they claim the above but have panic? i can see it leading to the same problems but adding an error msg to the end of it which can easily be abused. Am i missing something?

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  • How to implement a counter when using golang's goroutine?

    - by MrROY
    I'm trying to make a queue struct that have push and pop functions. I need to use 10 threads push and another 10 threads pop data, just like i did in the code below. Questions : 1. I need to print out how much i have pushed/popped, but i don't know how to do that. 2. Is there anyway to speed up my code ? the code is too slow for me. package main import ( "runtime" "time" ) const ( DATA_SIZE_PER_THREAD = 10000000 ) type Queue struct { records string } func (self Queue) push(record chan interface{}) { // need push counter record <- time.Now() } func (self Queue) pop(record chan interface{}) { // need pop counter <- record } func main() { runtime.GOMAXPROCS(runtime.NumCPU()) //record chan record := make(chan interface{},1000000) //finish flag chan finish := make(chan bool) queue := new(Queue) for i:=0; i<10; i++ { go func() { for j:=0; j<DATA_SIZE_PER_THREAD; j++ { queue.push(record) } finish<-true }() } for i:=0; i<10; i++ { go func() { for j:=0; j<DATA_SIZE_PER_THREAD; j++ { queue.pop(record) } finish<-true }() } for i:=0; i<20; i++ { <-finish } }

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  • MongoDB in Go (golang) with mgo: How do I update a record, find out if update was successful and get the data in a single atomic operation?

    - by Sebastián Grignoli
    I am using mgo driver for MongoDB under Go. My application asks for a task (with just a record select in Mongo from a collection called "jobs") and then registers itself as an asignee to complete that task (an update to that same "job" record, setting itself as assignee). The program will be running on several machines, all talking to the same Mongo. When my program lists the available tasks and then picks one, other instances might have already obtained that assignment, and the current assignment would have failed. How can I get sure that the record I read and then update does or does not have a certain value (in this case, an assignee) at the time of being updated? I am trying to get one assignment, no matter wich one, so I think I should first select a pending task and try to assign it, keeping it just in the case the updating was successful. So, my query should be something like: "From all records on collection 'jobs', update just one that has asignee=null, setting my ID as the assignee. Then, give me that record so I could run the job." How could I express that with mgo driver for Go?

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  • runtime error: invalid memory address or nil pointer dereference

    - by Klink
    I want to learn OpenGL 3.0 with golang. But when i try to compile some code, i get many errors. package main import ( "os" //"errors" "fmt" //gl "github.com/chsc/gogl/gl33" //"github.com/jteeuwen/glfw" "github.com/go-gl/gl" "github.com/go-gl/glfw" "runtime" "time" ) var ( width int = 640 height int = 480 ) var ( points = []float32{0.0, 0.8, -0.8, -0.8, 0.8, -0.8} ) func initScene() { gl.Init() gl.ClearColor(0.0, 0.5, 1.0, 1.0) gl.Enable(gl.CULL_FACE) gl.Viewport(0, 0, 800, 600) } func glfwInitWindowContext() { if err := glfw.Init(); err != nil { fmt.Fprintf(os.Stderr, "glfw_Init: %s\n", err) glfw.Terminate() } glfw.OpenWindowHint(glfw.FsaaSamples, 1) glfw.OpenWindowHint(glfw.WindowNoResize, 1) if err := glfw.OpenWindow(width, height, 0, 0, 0, 0, 32, 0, glfw.Windowed); err != nil { fmt.Fprintf(os.Stderr, "glfw_Window: %s\n", err) glfw.CloseWindow() } glfw.SetSwapInterval(1) glfw.SetWindowTitle("Title") } func drawScene() { for glfw.WindowParam(glfw.Opened) == 1 { gl.Clear(gl.COLOR_BUFFER_BIT) vertexShaderSrc := `#version 120 attribute vec2 coord2d; void main(void) { gl_Position = vec4(coord2d, 0.0, 1.0); }` vertexShader := gl.CreateShader(gl.VERTEX_SHADER) vertexShader.Source(vertexShaderSrc) vertexShader.Compile() fragmentShaderSrc := `#version 120 void main(void) { gl_FragColor[0] = 0.0; gl_FragColor[1] = 0.0; gl_FragColor[2] = 1.0; }` fragmentShader := gl.CreateShader(gl.FRAGMENT_SHADER) fragmentShader.Source(fragmentShaderSrc) fragmentShader.Compile() program := gl.CreateProgram() program.AttachShader(vertexShader) program.AttachShader(fragmentShader) program.Link() attribute_coord2d := program.GetAttribLocation("coord2d") program.Use() //attribute_coord2d.AttribPointer(size, typ, normalized, stride, pointer) attribute_coord2d.EnableArray() attribute_coord2d.AttribPointer(0, 3, false, 0, &(points[0])) //gl.DrawArrays(gl.TRIANGLES, 0, len(points)) gl.DrawArrays(gl.TRIANGLES, 0, 3) glfw.SwapBuffers() inputHandler() time.Sleep(100 * time.Millisecond) } } func inputHandler() { glfw.Enable(glfw.StickyKeys) if glfw.Key(glfw.KeyEsc) == glfw.KeyPress { //gl.DeleteBuffers(2, &uiVBO[0]) glfw.Terminate() } if glfw.Key(glfw.KeyF2) == glfw.KeyPress { glfw.SetWindowTitle("Title2") fmt.Println("Changed to 'Title2'") fmt.Println(len(points)) } if glfw.Key(glfw.KeyF1) == glfw.KeyPress { glfw.SetWindowTitle("Title1") fmt.Println("Changed to 'Title1'") } } func main() { runtime.LockOSThread() glfwInitWindowContext() initScene() drawScene() } And after that: panic: runtime error: invalid memory address or nil pointer dereference [signal 0xb code=0x1 addr=0x0 pc=0x41bc6f74] goroutine 1 [syscall]: github.com/go-gl/gl._Cfunc_glDrawArrays(0x4, 0x7f8500000003) /tmp/go-build463568685/github.com/go-gl/gl/_obj/_cgo_defun.c:610 +0x2f github.com/go-gl/gl.DrawArrays(0x4, 0x3, 0x0, 0x45bd70) /tmp/go-build463568685/github.com/go-gl/gl/_obj/gl.cgo1.go:1922 +0x33 main.drawScene() /home/klink/Dev/Go/gogl/gopher/exper.go:85 +0x1e6 main.main() /home/klink/Dev/Go/gogl/gopher/exper.go:116 +0x27 goroutine 2 [syscall]: created by runtime.main /build/buildd/golang-1/src/pkg/runtime/proc.c:221 exit status 2

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  • Support for non-english characters?

    - by TomJ
    Is support for non-english characters common in programming languages? I mean, technically, I would think it is feasable, but I don't have any experience in anything other than english, so I don't know how common it is. I know that there are non-english based programming languages, but can something like C#, C++, C, Java, or Python support non-english classes/methods/variables? Example in go (url, http://play.golang.org/p/wRYCNVdbjC) package main import "fmt" type ?? struct { ?? string } func main() { fmt.Println("Hello, ??") ?? := new(??) ??.?? = "hello world" fmt.Println(??.??) }

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  • Will Java be dead if the split into free/premium JVM happens?

    - by cringe
    According to http://www.theregister.co.uk/2010/11/06/oracle_dueling_jvms/ there is a possibility that Oracle really will kill Java split Java into Free and Premium JVMs. My Questions Do you think this will happen? Will this kill Java at the end? If you answer both questions with Yes, what are you doing about it? Which language would you choose, and which platform will you use? .NET/Mono? Plain compiled languages like Golang? Ruby? And if you answer No, why do you think Oracle will not harm Java and the community?

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  • Go - How to read/write to file?

    - by Seth Hoenig
    I've been trying to learn Go / Golang on my own, but I've been stumped on trying read and write to ordinary files. I can get as far as: inFile,_ := os.Open(INFILE,0,0); but actually getting the content of the file doesn't make sense, since the read function takes a []byte as a parameter?? func (file *File) Read(b []byte) (n int, err Error)

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  • Example about crypto/rand in Go

    - by nevalu
    Could put a little example about the use of crypto/rand [1]? The function Read has as parameter an array of bytes. Why? If it access to /dev/urandom to get the random data. func Read(b []byte) (n int, err os.Error) [1] http://golang.org/pkg/crypto/rand/

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