我试图找到一个关于init()函数在Go中的作用的精确解释。我读了Effective Go说的话，但我不确定我是否完全理解了它说的话。我不太确定的句子是:
finally的意思是最后:init是在包中所有变量声明都计算了它们的初始化式之后调用的，并且只有在所有导入的包都初始化之后才会计算这些初始化式。
包中所有变量声明对其初始化式求值意味着什么?这是否意味着如果你在一个包和它的文件中声明“全局”变量，init()将不会运行，直到所有的它被评估，然后它将运行所有的init函数，然后main()当。/main_file_name运行?
我还读了Mark Summerfield的书:
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。
在我的理解中，init()只在您打算运行main()时才相关，对吗?如果有人更清楚地理解init()，请随意纠正我
当前回答
在一个包中混合init函数执行顺序:
Const和变量定义的文件init()函数执行 初始化函数按文件名asc执行
其他回答
以你为其他用户设计的框架或库为例，这些用户最终会在他们的代码中有一个主函数来执行他们的应用程序。如果用户直接导入你库项目的子包，那么该子包的init将首先被调用(一次)。对于库的根包也是一样的，等等…
很多时候，您可能希望在不存在main func的情况下执行代码块，无论是否直接执行。
如果您作为虚拟库的开发人员，导入带有init函数的库的子包，它将首先被调用一次，您没有main func，但您需要确保一些变量或表将在调用其他函数之前初始化。
有一件事需要记住，不必担心，那就是: init总是在每个应用程序中执行一次。
Init执行发生:
就在“caller”包的init函数之前， 在main func函数之前， 但是在包级变量之后，var =[…]或者cost =[…]，
当你导入一个包时，它会按顺序运行所有的init函数。
我会给出一个很好的init函数的例子。它会将mime类型添加到一个名为mime的标准go库中，并且包级函数将直接使用mime标准包来获得已经在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
}
希望这对你和其他用户有所帮助，如果你有更多的问题，不要犹豫再次发帖!
是的，假设你有这个:
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()保证在调用init()之前运行，并且init()保证在调用main()之前运行。
请记住，init()总是被调用，无论是否有main，所以如果你导入一个包，它有init函数，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出现的顺序执行(当然是在所有变量初始化之后)。如果它们跨越多个文件，它们将按照词法文件名的顺序执行(正如@benc指出的那样):
init()函数似乎是按词法文件名顺序执行的。Go规范说:“构建系统被鼓励以词法文件名的顺序将属于同一个包的多个文件呈现给编译器”。似乎go build是这样工作的。
许多内部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
init()函数何时运行?
使用Go 1.16 (Q1 2021)，您将准确地看到它运行的时间以及运行多长时间。
参见从CL(更改列表)254659提交7c58ef7，修复问题41378。
Runtime: implement GODEBUG=inittrace=1 support Setting inittrace=1 causes the runtime to emit a single line to standard error for each package with init work, summarizing the execution time and memory allocation. The emitted debug information for init functions can be used to find bottlenecks or regressions in Go startup performance. Packages with no init function work (user defined or compiler generated) are omitted. Tracing plugin inits is not supported as they can execute concurrently. This would make the implementation of tracing more complex while adding support for a very rare use case. Plugin inits can be traced separately by testing a main package importing the plugins package imports explicitly. $ 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 ... Inspired by stapelberg@google.com who instrumented doInit in a prototype to measure init times with GDB.
还有一些建议:
只能有一个main()函数，但可以有很多init()函数。 你不需要显式地调用init()或main()，它们会自动调用。 Init()和main()不接受任何参数，也不返回任何东西。 Init()在main()之前运行。 如果你有很多init()，它们会按照声明的顺序运行。
看这张照片。：）
导入——> const——> var——> init()
如果一个包导入了其他包，则首先初始化导入的包。 当前包的常量初始化。 然后初始化当前包的变量。 最后，调用当前包的init()函数。
一个包可以有多个init函数(可以在单个文件中，也可以分布在多个文件中)，并且按照它们呈现给编译器的顺序调用它们。
一个包只能被初始化一次，即使它是从多个包中导入的。
