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using a label with anonymous function
New isn't a label, it's a field name in a sync.Pool type Pool struct { // New optionally specifies a function to generate // a value when Get would otherwise return nil. // It may not be changed concurrently with calls to Get. New func() interface{} // contains filtered or unexported fields } It's no different than N in the following example type T stru

Categories : Go

Install a Go binary, keep dependencies / packages
With go install, the package files (.a) are created in $GOPATH/pkg, with go build, I can't find the .a files anywhere. As mentioned in "How does the go build command work ?" The final step is to pack the object file into an archive file, .a, which the linker and the compiler consume. Because we invoked go build on a package, the result is discarded as $WORK is deleted after the build

Categories : Go

Reference a symbol in a Go package without knowing if you are in that package?
There is no such syntax. Observe the following things: Cyclical imports are forbidden. This especially means that a package cannot import itself. Thus, a package cannot refer to one of its symbols S with the pkg.S syntax because it will not be able to import itself. Even if you solved that problem, observe that packages can be given an arbitrary name once imported. For instance, you could do:

Categories : Go

Golang revel framework hot-reload in docker environment
Boot2docker uses VirtualBox, and I'm assuming vboxsf for shared folders. vboxsf doesn't notify about changed files. Try keeping the files completely inside the virtual machine. Does that help?

Categories : Go

Is it bad form to exclude godocs on exported names?
Note that golint would tell you that the doc for FrontPageView() must start with // FrontPageView ... And yes, it is good practice to include (here a short) comment on all exported methods, functions, as described also in "Go Code Review Comments". Comments documenting declarations should be full sentences, even if that seems a little redundant. This approach makes them format well when

Categories : Go

A use case for importing with blank identifier in golang
A use case is when what you want is only the init function doing some initialization (for example registering themselves so that you don't have to explictely call them). An exemple is the registring of some database drivers : import ( "database/sql" _ "github.com/ziutek/mymysql/godrv" )

Categories : Go

Which package contains merge function in golang
There isn't such a function in the standard library, you'll have to define it yourself. From your code, it seems that you've read this post which already gives an example of merge, a user-defined function: func merge(cs ...<-chan int) <-chan int { var wg sync.WaitGroup out := make(chan int) // Start an output goroutine for each input channel in cs. output // copies values

Categories : Go

Multiple response.WriteHeader calls in Go
The call to .WriteHeader() starts sending the response to the client over the net. Once the response is on its way, there is no way to back. The only thing you can do is to log the error locally (to let the server administrator know) or maybe to just fail silently. The 'Error()' function is used to send a complete HTTP (error) response, so you can only use this to replace sending your own respo

Categories : Go

Formatted errors.New
fmt.Errorf already does what you are trying to do. Looking at its source, you can see what went wrong: // Errorf formats according to a format specifier and returns the string // as a value that satisfies error. func Errorf(format string, a ...interface{}) error { return errors.New(Sprintf(format, a...)) } Note your code is missing the ... after a. From the spec: Passing arguments t

Categories : Go

How to convert a slice of one numeric type to another type
Go is quite low-level, this means that iterating through the slice is the most efficient method. Other languages may have built-in functions for such things, but all they do is iterate through the slice, there is no way to do it without the iteration. But there are some tricks, specifically use range and avoid indexing the slice as there is overhead in the out of bounds check. This would be the mo

Categories : Go

Package is found but contents are not?
argMap := config.parse(...); wouldn't work, since you declared a Parse() method. (as in "exported method configuration.Parse()") var config configuration.Config argMap := config.Parse(...); Config is exported, but the methods are case-sensitive (cf. Exported Identifiers).

Categories : Go

How do I make `go get` to build against x86_64 instead of i386
Set the environment variable GOARCH to the value amd64. This instructs the go command to generate files for amd64. Other valid values for GOARCH are 386 and arm.

Categories : Go

I can't run Go programs anymore
The Go Programming Language Specification Program execution A complete program is created by linking a single, unimported package called the main package with all the packages it imports, transitively. The main package must have package name main and declare a function main that takes no arguments and returns no value. func main() { … } Program execution begins by initi

Categories : Go

Which data types are inherently atomic
I don't believe that any of them are guaranteed to be atomic, but it's possible that some are in practice (of course, by atomic we mean that assigning to them simultaneously from two threads will produce one or the other value, and not some third value (such as a combination of the bits from each value) - we don't mean that you can atomically compare and store or something like that). Your best be

Categories : Go

Building Go binaries without debugging info
No, there isn't any way to do this right now. Also note that the -s option has been disabled for quite a while and does nothing. The comment about patching the runtime means that is currently the only way to disable that output. The runtime is what prints the stack traces on panic, and the segfault addresses; and you'd have to write a patch to disable that behavior.

Categories : Go

Generic variable for architecture-specific structs
If you simply want to pass these structs to json.MarshalIndent, the simple solution is to declare the variable as follows outside the if statement: var data interface{} It will be able to store either struct, and is the type expected by json.MarshalIndent. If you want to perform more operations that should work on either structure, consider defining an interface implemented by each struct, and

Categories : Go

RPC using UDP in GO
RPC over UDP requires special UDP aware handling due to the nature of UDP sockets. There is no connection, just datagrams sent to an address. For the client to get a reply, it would have to set up a listening socket and then send that to the server along with the request. The server would then reply to the clients address. net/rpc doesn't have any special case handling for non-connection orien

Categories : Go

FindStringSubmatch returns matched group twice
From Regexp.FindStringSubmatch: FindStringSubmatch returns a slice of strings holding the text of the leftmost match of the regular expression in s and the matches So: the first entry is what has been matched: '12334' (leftmost match) the second entry is the one captured group: '12334' Another example: re := regexp.MustCompile("a(x*)b(y|z)c") fmt.Printf("%q ", re.FindStringSubmatch("-ax

Categories : Go

GO language: fatal error: all goroutines are asleep - deadlock
Go program ends when the main function ends. From the language specification Program execution begins by initializing the main package and then invoking the function main. When that function invocation returns, the program exits. It does not wait for other (non-main) goroutines to complete. Therefore, you need to wait for your goroutines to finish. The common solution for this is to use syn

Categories : Go

Avoiding code duplication
A good article to refer to is "Middlewares in Go: Best practices and examples" The first code smell we encounter when writing a web application in Go is code duplication. Before processing the request, we will often need to log the request, convert app errors into HTTP 500 errors, authenticate users, etc. And we need to do most of these things for each handler. We could create a functio

Categories : Go

Gorilla mux routes in separate files in subfolder?
Here's general info on dealing with dependencies in Go. A key trick is, you just have to declare the Render variable in a package that your views can import. You could create a myapp/render package with a var Render that's either inited in the package itself (func init()) or set from main. But the context thing you found sounds totally sane, though it might be more than this app needs. The neat t

Categories : Go

Why does the "go run" command fail to find a second file in the main package?
Try providing all relevant files to go run $ go help run usage: go run [build flags] [-exec xprog] gofiles... [arguments...] Run compiles and runs the main package comprising the named Go source files. A Go source file is defined to be a file ending in a literal ".go" suffix.

Categories : Go

GO language: Reading a file and turning the content into an array
You can use ioutil.ReadFile to read the whole file as a string which is a json document and then Unmarshal the string into a struct that you will have made for easy access: type user_ip struct{ username string `json:"username"` ip string `json:"ip"` } type jsonStruct struct{ sample []user_ip } func main() { //you'll have to read file here str := `{ {

Categories : Go

How do I handle modified time with http.ServeContent()?
According to the documentation, If modtime is not the zero time, ServeContent includes it in a Last-Modified header in the response. If the request includes an If-Modified-Since header, ServeContent uses modtime to decide whether the content needs to be sent at all. So, depending on whether the client sends the If-Modified-Since header, this function will behave correctly or not. This seems

Categories : Go

golang and godep : Buildinstall after a golang dependency update when using godep?
FYI Since golang v1.4 I can now use the -a flag for the go install command, since it now longer tries to rebuild the standard library, see the v1.4 release notes section on the change to the build -a flag Obviously this does not apply in pre v1.4 as it will attempt to rebuild the standard library packages

Categories : Go

How to disable "exit status 1" when executing os.Exit(1)
To disable the message, don't use go run. go run is a tool to conveniently compile one or more go files into a temporary location, execute the binary, and clean up. Your executable is run in a sub-process, and the go tool is reporting the exit status for you.

Categories : Go

How to initialize a type with an underlying string value in go?
Convert the string to the correct type [conversions] http://play.golang.org/p/dkavI_QgPb s := "world" t := T(s) fmt.Println(t)

Categories : Go

Go with Sublime 3 returns "go run: no go files listed"
Save the file as tour.go (mind the extension .go). The command sublime tries to run is go run C:Users ew customerDesktopgoTour So it obviously does not have the right extension. The type in sublime does not really matter.

Categories : Go

use gob to package recursively defined structs
As of now, the encoding/gob package doesn't work with recursive values: Recursive types work fine, but recursive values (data with cycles) are problematic. This may change. Until this is changed, you'll have to either not use cyclic data, or use a different approach to serialisation.

Categories : Go

Overwrite anonymous struct function
Since Test has no ServeHTTP method, your test server uses Controller's, which calls Controller.Execute(). If you want it to work properly, define ServeHTTP for the Test type.

Categories : Go

Revel: "code does not compile: undefined: models"
You have imported your models using the dot (.) import qualifier. From the language spec: If an explicit period (.) appears instead of a name, all the package's exported identifiers will be declared in the current file's file block and can be accessed without a qualifier. This means you don't need to use models.TodoItem .. you can simply use TodoItem. That said .. I would suggest avoiding t

Categories : Go

A single or multiple gopaths for multiple projects using godep
I'm working on multiple projects depending on different versions of a certain package Then I would recommend a GOPATH per project, in order to better isolate each dependencies, and make sure there isn't any mix_up in said dependencies. Within each GOPATH, you still can use the dependency manager of your choice.

Categories : Go

Returning an optional value and an error
The convention in Go is to return (value, error) and if error != nil then value is (or may be) invalid. If you have special errors you need to do something with (like io.EOF) then making a specific error is normal practice. So I would say your 3rd example is the most idiomatic, if you want to do something different for ColorNotFound. var ColorNotFound = errors.New(...) func findColor(name stri

Categories : Go

Using Snappy compression on Gob data in Go?
package snappystream import "github.com/mreiferson/go-snappystream" snappystream wraps snappy-go and supplies a Reader and Writer for the snappy framed stream format. Have you considered package snappystream? For example, package main import ( "encoding/gob" "fmt" "os" "github.com/mreiferson/go-snappystream" ) type Object struct { Classifier struct{} } func (

Categories : Go

Golang return nil
This is similar to returning a nil error: see "Why is my nil error value not equal to nil? " Under the covers, interfaces are implemented as two elements, a type and a value. The value, called the interface's dynamic value, is an arbitrary concrete value and the type is that of the value. For the int value 3, an interface value contains, schematically, (int, 3). An interface value i

Categories : Go

type A satisfying requirements of type B
The DatabaseHandler satisfies the ChannelHandler interface with this method: func (d *databaseHandler) ProcessChannels(f *Feed, ch []*Channel) The interface requires: type ChannelHandler interface { ProcessChannels(f *Feed, newchannels []*Channel) }

Categories : Go

Safely terminating a request outside of handlefunc
I don't think trying to abort from within a function is what you want to do here. Instead, make the validation less repetitive. You could write something like package validate with func Require(form url.Values, required ...string) error, and, in your handler, if err := validate.Require(r.Form, "foo", "bar"); err != nil { ... }. Or you could do a more general validator: maybe take a map of field

Categories : Go

variable assignment in Golang
In queryDoc, err := bson.Marshal(something) you actually created a new queryDoc with := instead of =. The compiler didn't catch it because you have used it as well. Replace that with var err error queryDoc, err = bson.Marshal(something) and it should work as intended.

Categories : Go

Why a call to a user-defined String() for user-defined type throws "not enough arguments in call to BitFlag.String"?
You need to call String on an instance of BitFlag (here 'flag'), not on the BitFlag type itself. flag := Active | Send fmt.Println(strconv.Itoa(int(flag))) fmt.Println(flag.String()) See this play.golang.org example. Output: 3 3(Active|Send)

Categories : Go




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