I had trouble finding a list of what packages may be imported in the go playground at http://play.golang.org/. I was trying to use the (apparently experimental) package for ebnf. However even a short program won't import from golang.org (breaks on the import on line 4):
package main
import "fmt"
import "golang.org/x/exp/ebnf"
const g = `
Production = name "=" [ Expression ] "." .
Expression = Alternative { "|" Alternative } .
Alternative = Term { Term } .
Term = name | token [ "…" token ] | Group | Option | Repetition .
Group = "(" Expression ")" .
Option = "[" Expression "]" .
Repetition = "{" Expression "}" .`
func main() {
fmt.Println(g)
}
Is it stated anywhere that only base packages in golang.org/src/ would import (if that's the case)?
I'd really like to play with this experimental package and even non-experimental supplemental libraries like currency in the playground.
答案 0 :(得分：6)
The About button on the Playground gives some hint:
The playground can use most of the standard library, with some exceptions.
By the standard library the packages of the standard library are meant, which are listed on the Packages page, under the Standard library section. Packages listed under the Other section do not qualify (which is what you have tried - package golang.org/x/exp/ebnf falls under the experimental and deprecated packages listed under the Other category).
A must-read link if you want to know more about the Playground implementation:
The Go Blog: Inside the Go Playground
Here is an exhaustive playground test to import all the standard library packages to show they at least can be imported, but that doesn't mean everything (or even anything) can be reasonably used from them. The only package from the standard library that gives a compile error is runtime/cgo; "packages" without a buildable Go source file are not included for obvious reasons (because a folder is not a package if it does not contain at least one buildable Go source file).
Here's the Playground Link to try it yourself.
package main
import (
_ "archive/tar"
_ "archive/zip"
_ "bufio"
_ "bytes"
_ "compress/bzip2"
_ "compress/flate"
_ "compress/gzip"
_ "compress/lzw"
_ "compress/zlib"
_ "container/heap"
_ "container/list"
_ "container/ring"
_ "crypto"
_ "crypto/aes"
_ "crypto/cipher"
_ "crypto/des"
_ "crypto/dsa"
_ "crypto/ecdsa"
_ "crypto/elliptic"
_ "crypto/hmac"
_ "crypto/md5"
_ "crypto/rand"
_ "crypto/rc4"
_ "crypto/rsa"
_ "crypto/sha1"
_ "crypto/sha256"
_ "crypto/sha512"
_ "crypto/subtle"
_ "crypto/tls"
_ "crypto/x509"
_ "crypto/x509/pkix"
_ "database/sql"
_ "database/sql/driver"
_ "debug/dwarf"
_ "debug/elf"
_ "debug/gosym"
_ "debug/macho"
_ "debug/pe"
_ "debug/plan9obj"
_ "encoding"
_ "encoding/ascii85"
_ "encoding/asn1"
_ "encoding/base32"
_ "encoding/base64"
_ "encoding/binary"
_ "encoding/csv"
_ "encoding/gob"
_ "encoding/hex"
_ "encoding/json"
_ "encoding/pem"
_ "encoding/xml"
_ "errors"
_ "expvar"
_ "flag"
_ "fmt"
_ "go/ast"
_ "go/build"
_ "go/constant"
_ "go/doc"
_ "go/format"
_ "go/importer"
_ "go/parser"
_ "go/printer"
_ "go/scanner"
_ "go/token"
_ "go/types"
_ "hash"
_ "hash/adler32"
_ "hash/crc32"
_ "hash/crc64"
_ "hash/fnv"
_ "html"
_ "html/template"
_ "image"
_ "image/color"
_ "image/color/palette"
_ "image/draw"
_ "image/gif"
_ "image/jpeg"
_ "image/png"
_ "index/suffixarray"
_ "io"
_ "io/ioutil"
_ "log"
_ "log/syslog"
_ "math"
_ "math/big"
_ "math/cmplx"
_ "math/rand"
_ "mime"
_ "mime/multipart"
_ "mime/quotedprintable"
_ "net"
_ "net/http"
_ "net/http/cgi"
_ "net/http/cookiejar"
_ "net/http/fcgi"
_ "net/http/httptest"
_ "net/http/httputil"
_ "net/http/pprof"
_ "net/mail"
_ "net/rpc"
_ "net/rpc/jsonrpc"
_ "net/smtp"
_ "net/textproto"
_ "net/url"
_ "os"
_ "os/exec"
_ "os/signal"
_ "os/user"
_ "path"
_ "path/filepath"
_ "reflect"
_ "regexp"
_ "regexp/syntax"
_ "runtime"
// _ "runtime/cgo" // ERROR: missing Go type information
// for global symbol: .dynsym size 60
_ "runtime/debug"
_ "runtime/pprof"
_ "runtime/race"
_ "runtime/trace"
_ "sort"
_ "strconv"
_ "strings"
_ "sync"
_ "sync/atomic"
_ "syscall"
_ "testing"
_ "testing/iotest"
_ "testing/quick"
_ "text/scanner"
_ "text/tabwriter"
_ "text/template"
_ "text/template/parse"
_ "time"
_ "unicode"
_ "unicode/utf16"
_ "unicode/utf8"
_ "unsafe"
)
func main() {
println("ok")
}
答案 1 :(得分：1)
It appears to depend on the environment in which the playground is launched. The relevant code in the source seems to be the compileAndRun func, especially line 88:
cmd.Env = []string{"GOOS=nacl", "GOARCH=amd64p32", "GOPATH=" + os.Getenv("GOPATH")}
Which gets the GOPATH from the environment.
Other than that, the playground source does not have any explicit whitelist (or blacklist) of importable packages.
It's probably key to note that the compileAndRun func has no code to go get packages, so whatever is already in the GOPATH is what is available.
A perusal of the Makefile and Dockerfile does not reveal the specific deployment steps taken in the canonical http://play.golang.org site, so we simply have to rely on the documentation that Markus W Mahlberg pointed out; i.e. "a subset of the stdlib".
Also, you can deploy your own version of the go playground, and give it whatever GOPATH environment you choose.
答案 2 :(得分：0)
我在http://play.golang.org/的去游乐场中查找可以导入哪些软件包的列表很麻烦。
查找精确列表将比您现在（2019年5月16日）更加困难
GOPROXY 现在#golang游乐场支持多个文件：Example
这意味着您也可以有多个模块！现在
go.mod文件也已格式化：Example
package main
import (
"fmt"
"gopher.example/bar"
"play.ground/foo"
)
func main() {
fmt.Println(foo.Bar)
fmt.Println()
fmt.Println(bar.Baz)
fmt.Println()
fmt.Println("And go.mod files get formatted too. Try pressing the Format button!")
}
-- go.mod --
module "play.ground"
replace (
"gopher.example/bar" => ./bar
)
-- foo/foo.go --
package foo
const Bar = "The Go playground now has support for multiple files!"
-- bar/go.mod --
module gopher.example/bar
-- bar/bar.go --
package bar
const Baz = "Which means you can have multiple modules too!"