init() 函数何时运行？
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【中文标题】init() 函数何时运行？【英文标题】：When is the init() function run? 【发布时间】：2014-09-07 12:51:40 【问题描述】：我试图找到关于 init() 函数在 Go 中的作用的准确解释。我读了Effective Go 所说的内容，但我不确定我是否完全理解它所说的内容。我不确定的确切句子如下：
finally 的意思是 finally：在包中的所有变量声明都评估了它们的初始化器之后调用 init，并且只有在所有导入的包都被初始化之后才会评估它们。
all the variable declarations in the package have evaluated their initializers 是什么意思？这是否意味着如果您在包及其文件中声明“全局”变量， init() 将不会运行，直到所有它都被评估，然后它将运行所有 init 函数，然后在运行 ./main_file_name 时运行 main()？
我还阅读了 Mark Summerfield 的以下围棋书：
如果一个包有一个或多个 init() 函数，它们会在主包的 main() 函数被调用之前自动执行。
据我了解，init() 仅在您运行打算运行 main() 时才相关，对吗？或主包。任何人都更准确地理解init()随时纠正我
【问题讨论】：
使用 Go 1.16（2021 年第一季度）：GODEBUG=inittrace=1 go run（或 go test）。见my answer below。
【参考方案1】：
推荐的答案
Go Language
是的，假设你有 this:
var WhatIsThe = AnswerToLife()
func AnswerToLife() int // 1
return 42
func init() // 2
WhatIsThe = 0
func main() // 3
if WhatIsThe == 0
fmt.Println("It's all a lie.")
AnswerToLife() 保证在init() 被调用之前运行，init() 保证在main() 被调用之前运行。
记住init()总是被调用，不管是否有main，所以如果你导入一个有init函数的包，它将被执行。
此外，每个包可以有多个init() 函数；它们将按照它们在文件中显示的顺序执行（当然在所有变量都初始化之后）。如果它们跨越多个文件，它们将按词法文件名顺序执行（正如@benc 指出的那样）：
似乎
init()函数是按词法文件名顺序执行的。 Go 规范说“鼓励构建系统将属于同一个包的多个文件按照词法文件名顺序呈现给编译器”。go build似乎是这样工作的。
很多内部 Go 包使用 init() 来初始化表等，例如 https://github.com/golang/go/blob/883bc6/src/compress/bzip2/bzip2.go#L480
【讨论】：
init() 是每个包的东西，我认为......因此，这是否意味着如果不同的文件有自己的inits，所有 inint 总是在 main() 之前运行跑了吗？您能否还为我澄清一件事，为什么您会有一个没有 main 的 init() 以及它是如何工作的？这是否意味着 init() 是导入包之前运行的最后一件事？否则，如果它没有被导入并且没有主程序，程序将永远不会执行......对吗？ （除非我猜它是一个测试文件......）
在包没有main 的情况下运行 init 的原因有很多，例如，如果您需要初始化多个变量或加载一些文件或进行一次性计算。现在，如果您的整个程序是一个并不真正需要的包，但是如果它是多个包，其中一些可能需要针对它进行一些初始化。
@Pinocchio 当你执行一个 go 程序时，总会有一个（而且只有一个）main()。并且 init() 函数在那个 main() 之前运行。然而，并不是所有的包都需要一个 main()。如果例如您正在创建一个具有用于连接数据库的实用程序功能的可重用包，该包不应该有 main()。但它可能有一个 init()。当您在程序中使用该数据库包时，该程序将有一个 main()。
init 的一个很好的例子是具有可插拔架构，例如 Cobra commander。请注意示例中如何引用init
@OneOfOne 经过几次测试，似乎 init() 函数是按词法文件名顺序执行的。 Go spec 表示“鼓励构建系统将属于同一包的多个文件按照词法文件名顺序呈现给编译器”。 go build 似乎是这样工作的。【参考方案2】：
要添加的东西（我会添加作为评论，但写这篇文章的时候我还没有足够的声誉）
在同一个包中有多个初始化我还没有找到任何有保证的方法来知道它们将以什么顺序运行。例如我有：
package config
- config.go
- router.go
config.go 和 router.go 都包含 init() 函数，但是在运行 router.go 的函数时首先运行（这导致我的应用程序崩溃）。
如果您有多个文件，每个文件都有自己的init() 函数，请务必注意，不能保证您先获得一个。最好使用变量赋值，如OneToOne 在他的示例中所示。最好的部分是：此变量声明将发生在包中的所有 init() 函数之前。
例如
config.go:
var ConfigSuccess = configureApplication()
func init()
doSomething()
func configureApplication() bool
l4g.Info("Configuring application...")
if valid := loadCommandLineFlags(); !valid
l4g.Critical("Failed to load Command Line Flags")
return false
return true
router.go:
func init()
var (
rwd string
tmp string
ok bool
)
if metapath, ok := Config["fs"]["metapath"].(string); ok
var err error
Conn, err = services.NewConnection(metapath + "/metadata.db")
if err != nil
panic(err)
无论var ConfigSuccess = configureApplication() 是否存在于router.go 或config.go 中，它都会在init() 运行之前运行。
【讨论】：
只是我的两分钱：您可以将“简单初始化”与复杂（引发恐慌）初始化分开。如果您对 init() 感到恐慌，那么您就没有给主程序机会。也许func initialize|loadConfig|connect 与func init 分开，留下func init() 用于基本的东西（没有恐慌）。这种分离还消除了 hack 以确保 init 顺序的需要。希望对您有所帮助。
引用语言规范：没有导入的包通过为其所有包级变量分配初始值来初始化，然后按照它们在源中出现的顺序调用所有 init 函数，可能在多个文件，如提交给编译器。为了确保可重现的初始化行为，鼓励构建系统将属于同一个包的多个文件按照词法文件名顺序呈现给编译器。
我在我的应用程序中遇到的不幸的事情是它没有按词法顺序执行初始化函数。这可能是一个编译器错误，此后已被修复。我没有费心去检查是否有任何与此相关的问题。
来自上述 updogliu 的重要评论。当涉及进口时，这似乎并不成立。在这里遇到一个案例，我有一个依赖于多个导入包的测试。并且使用包级变量的技巧并不能帮助我防止依赖包上的 init() 方法在我的变量分配函数之前运行。
单个包中init() 调用的顺序取决于它们被输入编译器的方式； go 工具按字母顺序排列文件。从那时起，它们在单个文件中按语法顺序进行初始化。 为单词选择而编辑【参考方案3】：
https://golang.org/ref/mem#tmp_4
程序初始化在单个 goroutine 中运行，但该 goroutine 可能会创建其他并发运行的 goroutine。
如果包 p 导入包 q，q 的 init 函数的完成发生在任何 p 的开始之前。
main.main 函数的开始发生在所有 init 函数完成之后。
【讨论】：
【参考方案4】：以您为其他用户设计的框架或库为例，这些用户最终将在他们的代码中包含main function 以执行他们的应用程序。如果用户直接导入库项目的子包，那么该子包的init 将首先被调用（一次）。库的根包等也是如此……
很多时候您可能希望在不存在main func 的情况下直接或不直接执行代码块。
如果你作为虚构库的开发者，导入你的库的子包有init函数，它会先被调用一次，你没有@ 987654325@ 但是你需要确保一些变量，或者一个表，在调用其他函数之前会被初始化。
要记住而不用担心的一件好事是：
init 始终在每个应用程序中执行一次。
init 执行发生：
-
就在“调用者”包的
init 函数之前，
在main func 之前，可选地，
但在包级变量之后，var = [...] or cost = [...]，
当你导入一个包时，它会按顺序运行它的所有初始化函数。
我将给出一个很好的初始化函数示例。它将 mime 类型添加到名为 mime 的标准 go 库中，并且包级函数将直接使用 mime 标准包来获取已经在其 init 函数中初始化的自定义 mime 类型：
package mime
import (
"mime"
"path/filepath"
)
var types = map[string]string
".3dm": "x-world/x-3dmf",
".3dmf": "x-world/x-3dmf",
".7z": "application/x-7z-compressed",
".a": "application/octet-stream",
".aab": "application/x-authorware-bin",
".aam": "application/x-authorware-map",
".aas": "application/x-authorware-seg",
".abc": "text/vndabc",
".ace": "application/x-ace-compressed",
".acgi": "text/html",
".afl": "video/animaflex",
".ai": "application/postscript",
".aif": "audio/aiff",
".aifc": "audio/aiff",
".aiff": "audio/aiff",
".aim": "application/x-aim",
".aip": "text/x-audiosoft-intra",
".alz": "application/x-alz-compressed",
".ani": "application/x-navi-animation",
".aos": "application/x-nokia-9000-communicator-add-on-software",
".aps": "application/mime",
".apk": "application/vnd.android.package-archive",
".arc": "application/x-arc-compressed",
".arj": "application/arj",
".art": "image/x-jg",
".asf": "video/x-ms-asf",
".asm": "text/x-asm",
".asp": "text/asp",
".asx": "application/x-mplayer2",
".au": "audio/basic",
".avi": "video/x-msvideo",
".avs": "video/avs-video",
".bcpio": "application/x-bcpio",
".bin": "application/mac-binary",
".bmp": "image/bmp",
".boo": "application/book",
".book": "application/book",
".boz": "application/x-bzip2",
".bsh": "application/x-bsh",
".bz2": "application/x-bzip2",
".bz": "application/x-bzip",
".c++": "text/plain",
".c": "text/x-c",
".cab": "application/vnd.ms-cab-compressed",
".cat": "application/vndms-pkiseccat",
".cc": "text/x-c",
".ccad": "application/clariscad",
".cco": "application/x-cocoa",
".cdf": "application/cdf",
".cer": "application/pkix-cert",
".cha": "application/x-chat",
".chat": "application/x-chat",
".chrt": "application/vnd.kde.kchart",
".class": "application/java",
".com": "text/plain",
".conf": "text/plain",
".cpio": "application/x-cpio",
".cpp": "text/x-c",
".cpt": "application/mac-compactpro",
".crl": "application/pkcs-crl",
".crt": "application/pkix-cert",
".crx": "application/x-chrome-extension",
".csh": "text/x-scriptcsh",
".css": "text/css",
".csv": "text/csv",
".cxx": "text/plain",
".dar": "application/x-dar",
".dcr": "application/x-director",
".deb": "application/x-debian-package",
".deepv": "application/x-deepv",
".def": "text/plain",
".der": "application/x-x509-ca-cert",
".dif": "video/x-dv",
".dir": "application/x-director",
".divx": "video/divx",
".dl": "video/dl",
".dmg": "application/x-apple-diskimage",
".doc": "application/msword",
".dot": "application/msword",
".dp": "application/commonground",
".drw": "application/drafting",
".dump": "application/octet-stream",
".dv": "video/x-dv",
".dvi": "application/x-dvi",
".dwf": "drawing/x-dwf=(old)",
".dwg": "application/acad",
".dxf": "application/dxf",
".dxr": "application/x-director",
".el": "text/x-scriptelisp",
".elc": "application/x-bytecodeelisp=(compiled=elisp)",
".eml": "message/rfc822",
".env": "application/x-envoy",
".eps": "application/postscript",
".es": "application/x-esrehber",
".etx": "text/x-setext",
".evy": "application/envoy",
".exe": "application/octet-stream",
".f77": "text/x-fortran",
".f90": "text/x-fortran",
".f": "text/x-fortran",
".fdf": "application/vndfdf",
".fif": "application/fractals",
".fli": "video/fli",
".flo": "image/florian",
".flv": "video/x-flv",
".flx": "text/vndfmiflexstor",
".fmf": "video/x-atomic3d-feature",
".for": "text/x-fortran",
".fpx": "image/vndfpx",
".frl": "application/freeloader",
".funk": "audio/make",
".g3": "image/g3fax",
".g": "text/plain",
".gif": "image/gif",
".gl": "video/gl",
".gsd": "audio/x-gsm",
".gsm": "audio/x-gsm",
".gsp": "application/x-gsp",
".gss": "application/x-gss",
".gtar": "application/x-gtar",
".gz": "application/x-compressed",
".gzip": "application/x-gzip",
".h": "text/x-h",
".hdf": "application/x-hdf",
".help": "application/x-helpfile",
".hgl": "application/vndhp-hpgl",
".hh": "text/x-h",
".hlb": "text/x-script",
".hlp": "application/hlp",
".hpg": "application/vndhp-hpgl",
".hpgl": "application/vndhp-hpgl",
".hqx": "application/binhex",
".hta": "application/hta",
".htc": "text/x-component",
".htm": "text/html",
".html": "text/html",
".htmls": "text/html",
".htt": "text/webviewhtml",
".htx": "text/html",
".ice": "x-conference/x-cooltalk",
".ico": "image/x-icon",
".ics": "text/calendar",
".icz": "text/calendar",
".idc": "text/plain",
".ief": "image/ief",
".iefs": "image/ief",
".iges": "application/iges",
".igs": "application/iges",
".ima": "application/x-ima",
".imap": "application/x-httpd-imap",
".inf": "application/inf",
".ins": "application/x-internett-signup",
".ip": "application/x-ip2",
".isu": "video/x-isvideo",
".it": "audio/it",
".iv": "application/x-inventor",
".ivr": "i-world/i-vrml",
".ivy": "application/x-livescreen",
".jam": "audio/x-jam",
".jav": "text/x-java-source",
".java": "text/x-java-source",
".jcm": "application/x-java-commerce",
".jfif-tbnl": "image/jpeg",
".jfif": "image/jpeg",
".jnlp": "application/x-java-jnlp-file",
".jpe": "image/jpeg",
".jpeg": "image/jpeg",
".jpg": "image/jpeg",
".jps": "image/x-jps",
".js": "application/javascript",
".json": "application/json",
".jut": "image/jutvision",
".kar": "audio/midi",
".karbon": "application/vnd.kde.karbon",
".kfo": "application/vnd.kde.kformula",
".flw": "application/vnd.kde.kivio",
".kml": "application/vnd.google-earth.kml+xml",
".kmz": "application/vnd.google-earth.kmz",
".kon": "application/vnd.kde.kontour",
".kpr": "application/vnd.kde.kpresenter",
".kpt": "application/vnd.kde.kpresenter",
".ksp": "application/vnd.kde.kspread",
".kwd": "application/vnd.kde.kword",
".kwt": "application/vnd.kde.kword",
".ksh": "text/x-scriptksh",
".la": "audio/nspaudio",
".lam": "audio/x-liveaudio",
".latex": "application/x-latex",
".lha": "application/lha",
".lhx": "application/octet-stream",
".list": "text/plain",
".lma": "audio/nspaudio",
".log": "text/plain",
".lsp": "text/x-scriptlisp",
".lst": "text/plain",
".lsx": "text/x-la-asf",
".ltx": "application/x-latex",
".lzh": "application/octet-stream",
".lzx": "application/lzx",
".m1v": "video/mpeg",
".m2a": "audio/mpeg",
".m2v": "video/mpeg",
".m3u": "audio/x-mpegurl",
".m": "text/x-m",
".man": "application/x-troff-man",
".manifest": "text/cache-manifest",
".map": "application/x-navimap",
".mar": "text/plain",
".mbd": "application/mbedlet",
".mc$": "application/x-magic-cap-package-10",
".mcd": "application/mcad",
".mcf": "text/mcf",
".mcp": "application/netmc",
".me": "application/x-troff-me",
".mht": "message/rfc822",
".mhtml": "message/rfc822",
".mid": "application/x-midi",
".midi": "application/x-midi",
".mif": "application/x-frame",
".mime": "message/rfc822",
".mjf": "audio/x-vndaudioexplosionmjuicemediafile",
".mjpg": "video/x-motion-jpeg",
".mm": "application/base64",
".mme": "application/base64",
".mod": "audio/mod",
".moov": "video/quicktime",
".mov": "video/quicktime",
".movie": "video/x-sgi-movie",
".mp2": "audio/mpeg",
".mp3": "audio/mpeg3",
".mp4": "video/mp4",
".mpa": "audio/mpeg",
".mpc": "application/x-project",
".mpe": "video/mpeg",
".mpeg": "video/mpeg",
".mpg": "video/mpeg",
".mpga": "audio/mpeg",
".mpp": "application/vndms-project",
".mpt": "application/x-project",
".mpv": "application/x-project",
".mpx": "application/x-project",
".mrc": "application/marc",
".ms": "application/x-troff-ms",
".mv": "video/x-sgi-movie",
".my": "audio/make",
".mzz": "application/x-vndaudioexplosionmzz",
".nap": "image/naplps",
".naplps": "image/naplps",
".nc": "application/x-netcdf",
".ncm": "application/vndnokiaconfiguration-message",
".nif": "image/x-niff",
".niff": "image/x-niff",
".nix": "application/x-mix-transfer",
".nsc": "application/x-conference",
".nvd": "application/x-navidoc",
".o": "application/octet-stream",
".oda": "application/oda",
".odb": "application/vnd.oasis.opendocument.database",
".odc": "application/vnd.oasis.opendocument.chart",
".odf": "application/vnd.oasis.opendocument.formula",
".odg": "application/vnd.oasis.opendocument.graphics",
".odi": "application/vnd.oasis.opendocument.image",
".odm": "application/vnd.oasis.opendocument.text-master",
".odp": "application/vnd.oasis.opendocument.presentation",
".ods": "application/vnd.oasis.opendocument.spreadsheet",
".odt": "application/vnd.oasis.opendocument.text",
".oga": "audio/ogg",
".ogg": "audio/ogg",
".ogv": "video/ogg",
".omc": "application/x-omc",
".omcd": "application/x-omcdatamaker",
".omcr": "application/x-omcregerator",
".otc": "application/vnd.oasis.opendocument.chart-template",
".otf": "application/vnd.oasis.opendocument.formula-template",
".otg": "application/vnd.oasis.opendocument.graphics-template",
".oth": "application/vnd.oasis.opendocument.text-web",
".oti": "application/vnd.oasis.opendocument.image-template",
".otm": "application/vnd.oasis.opendocument.text-master",
".otp": "application/vnd.oasis.opendocument.presentation-template",
".ots": "application/vnd.oasis.opendocument.spreadsheet-template",
".ott": "application/vnd.oasis.opendocument.text-template",
".p10": "application/pkcs10",
".p12": "application/pkcs-12",
".p7a": "application/x-pkcs7-signature",
".p7c": "application/pkcs7-mime",
".p7m": "application/pkcs7-mime",
".p7r": "application/x-pkcs7-certreqresp",
".p7s": "application/pkcs7-signature",
".p": "text/x-pascal",
".part": "application/pro_eng",
".pas": "text/pascal",
".pbm": "image/x-portable-bitmap",
".pcl": "application/vndhp-pcl",
".pct": "image/x-pict",
".pcx": "image/x-pcx",
".pdb": "chemical/x-pdb",
".pdf": "application/pdf",
".pfunk": "audio/make",
".pgm": "image/x-portable-graymap",
".pic": "image/pict",
".pict": "image/pict",
".pkg": "application/x-newton-compatible-pkg",
".pko": "application/vndms-pkipko",
".pl": "text/x-scriptperl",
".plx": "application/x-pixclscript",
".pm4": "application/x-pagemaker",
".pm5": "application/x-pagemaker",
".pm": "text/x-scriptperl-module",
".png": "image/png",
".pnm": "application/x-portable-anymap",
".pot": "application/mspowerpoint",
".pov": "model/x-pov",
".ppa": "application/vndms-powerpoint",
".ppm": "image/x-portable-pixmap",
".pps": "application/mspowerpoint",
".ppt": "application/mspowerpoint",
".ppz": "application/mspowerpoint",
".pre": "application/x-freelance",
".prt": "application/pro_eng",
".ps": "application/postscript",
".psd": "application/octet-stream",
".pvu": "paleovu/x-pv",
".pwz": "application/vndms-powerpoint",
".py": "text/x-scriptphyton",
".pyc": "application/x-bytecodepython",
".qcp": "audio/vndqcelp",
".qd3": "x-world/x-3dmf",
".qd3d": "x-world/x-3dmf",
".qif": "image/x-quicktime",
".qt": "video/quicktime",
".qtc": "video/x-qtc",
".qti": "image/x-quicktime",
".qtif": "image/x-quicktime",
".ra": "audio/x-pn-realaudio",
".ram": "audio/x-pn-realaudio",
".rar": "application/x-rar-compressed",
".ras": "application/x-cmu-raster",
".rast": "image/cmu-raster",
".rexx": "text/x-scriptrexx",
".rf": "image/vndrn-realflash",
".rgb": "image/x-rgb",
".rm": "application/vndrn-realmedia",
".rmi": "audio/mid",
".rmm": "audio/x-pn-realaudio",
".rmp": "audio/x-pn-realaudio",
".rng": "application/ringing-tones",
".rnx": "application/vndrn-realplayer",
".roff": "application/x-troff",
".rp": "image/vndrn-realpix",
".rpm": "audio/x-pn-realaudio-plugin",
".rt": "text/vndrn-realtext",
".rtf": "text/richtext",
".rtx": "text/richtext",
".rv": "video/vndrn-realvideo",
".s": "text/x-asm",
".s3m": "audio/s3m",
".s7z": "application/x-7z-compressed",
".saveme": "application/octet-stream",
".sbk": "application/x-tbook",
".scm": "text/x-scriptscheme",
".sdml": "text/plain",
".sdp": "application/sdp",
".sdr": "application/sounder",
".sea": "application/sea",
".set": "application/set",
".sgm": "text/x-sgml",
".sgml": "text/x-sgml",
".sh": "text/x-scriptsh",
".shar": "application/x-bsh",
".shtml": "text/x-server-parsed-html",
".sid": "audio/x-psid",
".skd": "application/x-koan",
".skm": "application/x-koan",
".skp": "application/x-koan",
".skt": "application/x-koan",
".sit": "application/x-stuffit",
".sitx": "application/x-stuffitx",
".sl": "application/x-seelogo",
".smi": "application/smil",
".smil": "application/smil",
".snd": "audio/basic",
".sol": "application/solids",
".spc": "text/x-speech",
".spl": "application/futuresplash",
".spr": "application/x-sprite",
".sprite": "application/x-sprite",
".spx": "audio/ogg",
".src": "application/x-wais-source",
".ssi": "text/x-server-parsed-html",
".ssm": "application/streamingmedia",
".sst": "application/vndms-pkicertstore",
".step": "application/step",
".stl": "application/sla",
".stp": "application/step",
".sv4cpio": "application/x-sv4cpio",
".sv4crc": "application/x-sv4crc",
".svf": "image/vnddwg",
".svg": "image/svg+xml",
".svr": "application/x-world",
".swf": "application/x-shockwave-flash",
".t": "application/x-troff",
".talk": "text/x-speech",
".tar": "application/x-tar",
".tbk": "application/toolbook",
".tcl": "text/x-scripttcl",
".tcsh": "text/x-scripttcsh",
".tex": "application/x-tex",
".texi": "application/x-texinfo",
".texinfo": "application/x-texinfo",
".text": "text/plain",
".tgz": "application/gnutar",
".tif": "image/tiff",
".tiff": "image/tiff",
".tr": "application/x-troff",
".tsi": "audio/tsp-audio",
".tsp": "application/dsptype",
".tsv": "text/tab-separated-values",
".turbot": "image/florian",
".txt": "text/plain",
".uil": "text/x-uil",
".uni": "text/uri-list",
".unis": "text/uri-list",
".unv": "application/i-deas",
".uri": "text/uri-list",
".uris": "text/uri-list",
".ustar": "application/x-ustar",
".uu": "text/x-uuencode",
".uue": "text/x-uuencode",
".vcd": "application/x-cdlink",
".vcf": "text/x-vcard",
".vcard": "text/x-vcard",
".vcs": "text/x-vcalendar",
".vda": "application/vda",
".vdo": "video/vdo",
".vew": "application/groupwise",
".viv": "video/vivo",
".vivo": "video/vivo",
".vmd": "application/vocaltec-media-desc",
".vmf": "application/vocaltec-media-file",
".voc": "audio/voc",
".vos": "video/vosaic",
".vox": "audio/voxware",
".vqe": "audio/x-twinvq-plugin",
".vqf": "audio/x-twinvq",
".vql": "audio/x-twinvq-plugin",
".vrml": "application/x-vrml",
".vrt": "x-world/x-vrt",
".vsd": "application/x-visio",
".vst": "application/x-visio",
".vsw": "application/x-visio",
".w60": "application/wordperfect60",
".w61": "application/wordperfect61",
".w6w": "application/msword",
".wav": "audio/wav",
".wb1": "application/x-qpro",
".wbmp": "image/vnd.wap.wbmp",
".web": "application/vndxara",
".wiz": "application/msword",
".wk1": "application/x-123",
".wmf": "windows/metafile",
".wml": "text/vnd.wap.wml",
".wmlc": "application/vnd.wap.wmlc",
".wmls": "text/vnd.wap.wmlscript",
".wmlsc": "application/vnd.wap.wmlscriptc",
".word": "application/msword",
".wp5": "application/wordperfect",
".wp6": "application/wordperfect",
".wp": "application/wordperfect",
".wpd": "application/wordperfect",
".wq1": "application/x-lotus",
".wri": "application/mswrite",
".wrl": "application/x-world",
".wrz": "model/vrml",
".wsc": "text/scriplet",
".wsrc": "application/x-wais-source",
".wtk": "application/x-wintalk",
".x-png": "image/png",
".xbm": "image/x-xbitmap",
".xdr": "video/x-amt-demorun",
".xgz": "xgl/drawing",
".xif": "image/vndxiff",
".xl": "application/excel",
".xla": "application/excel",
".xlb": "application/excel",
".xlc": "application/excel",
".xld": "application/excel",
".xlk": "application/excel",
".xll": "application/excel",
".xlm": "application/excel",
".xls": "application/excel",
".xlt": "application/excel",
".xlv": "application/excel",
".xlw": "application/excel",
".xm": "audio/xm",
".xml": "text/xml",
".xmz": "xgl/movie",
".xpix": "application/x-vndls-xpix",
".xpm": "image/x-xpixmap",
".xsr": "video/x-amt-showrun",
".xwd": "image/x-xwd",
".xyz": "chemical/x-pdb",
".z": "application/x-compress",
".zip": "application/zip",
".zoo": "application/octet-stream",
".zsh": "text/x-scriptzsh",
".docx": "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
".docm": "application/vnd.ms-word.document.macroEnabled.12",
".dotx": "application/vnd.openxmlformats-officedocument.wordprocessingml.template",
".dotm": "application/vnd.ms-word.template.macroEnabled.12",
".xlsx": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
".xlsm": "application/vnd.ms-excel.sheet.macroEnabled.12",
".xltx": "application/vnd.openxmlformats-officedocument.spreadsheetml.template",
".xltm": "application/vnd.ms-excel.template.macroEnabled.12",
".xlsb": "application/vnd.ms-excel.sheet.binary.macroEnabled.12",
".xlam": "application/vnd.ms-excel.addin.macroEnabled.12",
".pptx": "application/vnd.openxmlformats-officedocument.presentationml.presentation",
".pptm": "application/vnd.ms-powerpoint.presentation.macroEnabled.12",
".ppsx": "application/vnd.openxmlformats-officedocument.presentationml.slideshow",
".ppsm": "application/vnd.ms-powerpoint.slideshow.macroEnabled.12",
".potx": "application/vnd.openxmlformats-officedocument.presentationml.template",
".potm": "application/vnd.ms-powerpoint.template.macroEnabled.12",
".ppam": "application/vnd.ms-powerpoint.addin.macroEnabled.12",
".sldx": "application/vnd.openxmlformats-officedocument.presentationml.slide",
".sldm": "application/vnd.ms-powerpoint.slide.macroEnabled.12",
".thmx": "application/vnd.ms-officetheme",
".onetoc": "application/onenote",
".onetoc2": "application/onenote",
".onetmp": "application/onenote",
".onepkg": "application/onenote",
".xpi": "application/x-xpinstall",
func init()
for ext, typ := range types
// skip errors
mime.AddExtensionType(ext, typ)
// typeByExtension returns the MIME type associated with the file extension ext.
// The extension ext should begin with a leading dot, as in ".html".
// When ext has no associated type, typeByExtension returns "".
//
// Extensions are looked up first case-sensitively, then case-insensitively.
//
// The built-in table is small but on unix it is augmented by the local
// system's mime.types file(s) if available under one or more of these
// names:
//
// /etc/mime.types
// /etc/apache2/mime.types
// /etc/apache/mime.types
//
// On Windows, MIME types are extracted from the registry.
//
// Text types have the charset parameter set to "utf-8" by default.
func TypeByExtension(fullfilename string) string
ext := filepath.Ext(fullfilename)
typ := mime.TypeByExtension(ext)
// mime.TypeByExtension returns as text/plain; | charset=utf-8 the static .js (not always)
if ext == ".js" && (typ == "text/plain" || typ == "text/plain; charset=utf-8")
if ext == ".js"
typ = "application/javascript"
return typ
希望对您和其他用户有所帮助，如果您有更多问题，请不要犹豫再次发布！
【讨论】：
【参考方案5】：init 函数先运行，然后再运行 main。它用于在程序运行之前先设置一些东西，例如：
访问模板， 使用所有内核运行程序， 检查 Goos 和拱门等...
【讨论】：
【参考方案6】：init 会在任何使用它的包的地方被调用（无论是空白导入还是导入），但只会调用一次。
这是一个包裹：
package demo
import (
"some/logs"
)
var count int
func init()
logs.Debug(count)
// Do do
func Do()
logs.Debug("dd")
任何包（主包或任何测试包）将其导入为空白：
_ "printfcoder.com/we/models/demo"
或使用它导入它 func:
"printfcoder.com/we/models/demo"
func someFunc()
demo.Do()
init 只会记录一次0。
第一个使用它的包，它的 init 函数将在包的 init 之前运行。所以：
A调用B，B调用C，都有init func，C的init在B之前，B在A之前。
【讨论】：
【参考方案7】：这是另一个例子 - https://play.golang.org/p/9P-LmSkUMKY
package main
import (
"fmt"
)
func callOut() int
fmt.Println("Outside is beinge executed")
return 1
var test = callOut()
func init()
fmt.Println("Init3 is being executed")
func init()
fmt.Println("Init is being executed")
func init()
fmt.Println("Init2 is being executed")
func main()
fmt.Println("Do your thing !")
上述程序的输出
$ go run init/init.go
Outside is being executed
Init3 is being executed
Init is being executed
Init2 is being executed
Do your thing !
【讨论】：
【参考方案8】：mutil init 函数在一个包中执行顺序：
常量和变量定义的文件init()函数执行
init函数按文件名asc执行顺序
【讨论】：
【参考方案9】：看这张照片。 :)
import --> const --> var --> init()
如果一个包导入其他包，首先初始化导入的包。
然后初始化当前包的常量。
然后初始化当前包的变量。
最后调用了当前包的init()函数。
一个包可以有多个 init 函数（在单个文件中或分布在多个文件中），它们按照它们呈现给编译器的顺序被调用。
一个包即使是从多个包导入的，也只会初始化一次。
【讨论】：
谢谢。为这个图表添加一些文本是有意义的。 我不太确定我们是否可以说常量被初始化。他们应该在编译时就知道了，对吧？ 谢谢，这张图片帮助我解决了一个主要的构建问题，但我能问一下这张图片的来源吗？ @KoredeLawrenceOluwafemi 查看图片链接你会发现它来自中国围棋布道者github.com/astaxie写的book 并且它们按照它们呈现给编译器的顺序被调用：在大多数情况下，它们按照文件名的顺序调用，A.go, a.go, d.go, .... 【参考方案10】：更多提示：
main() 函数只能有 1 个，但 init() 函数可以有多个。 您无需显式调用 init() 或 main()，它们会自动调用。 init() 和 main() 不接受任何参数，也不返回任何内容。 init() 在 main() 之前运行。 如果您有多个 init()，它们会按照声明的顺序运行。
【讨论】：
【参考方案11】：
init()函数何时运行？
使用 Go 1.16（2021 年第一季度），您将准确地看到它何时运行以及运行多长时间。
从CL (Change List) 254659 看到commit 7c58ef7，修复issue 41378。
运行时：实现
GODEBUG=inittrace=1支持设置
inittrace=1会导致运行时向标准错误发出单行 每个包都有 init 工作，总结执行时间和内存分配。
init函数发出的调试信息可用于查找瓶颈 或 Go 启动性能的回归。没有
init函数工作（用户定义或编译器生成）的包将被忽略。不支持跟踪插件初始化，因为它们可以同时执行。这个会 使跟踪的实现更加复杂，同时添加对非常罕见的支持 用例。插件初始化可以通过测试主包导入来单独跟踪 插件包显式导入。
$ GODEBUG=inittrace=1 go test init internal/bytealg @0.008 ms, 0 ms clock, 0 bytes, 0 allocs init runtime @0.059 ms, 0.026 ms clock, 0 bytes, 0 allocs init math @0.19 ms, 0.001 ms clock, 0 bytes, 0 allocs init errors @0.22 ms, 0.004 ms clock, 0 bytes, 0 allocs init strconv @0.24 ms, 0.002 ms clock, 32 bytes, 2 allocs init sync @0.28 ms, 0.003 ms clock, 16 bytes, 1 allocs init unicode @0.44 ms, 0.11 ms clock, 23328 bytes, 24 allocs ...灵感来自 stapelberg@google.com，他使用了
doInit在原型中使用 GDB 测量init次。
【讨论】：
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