Go use global variables be careful with closures

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2015-03-16

Go use global variables be careful with closures

Here is a simple recurrence:

package mainimport (    "fmt"    "net/http")type Logger struct{}func (this *Logger) Debug() {    if this == nil {        panic("fuck")    }    fmt.Println("hello world")}var __logger *Loggerfunc AppLog() *Logger {    return __logger}func InitConf() {    __logger = &Logger{}}// ------内上内容应该是写在log包中，这里是方便演示------var logger = AppLog()func HelloWorld(w http.ResponseWriter, r *http.Request) {    AppLog().Debug() // ok    logger.Debug()   // panic}func main() {    InitConf()    http.HandleFunc("/", HelloWorld)    http.ListenAndServe(":8088", nil)}

Will collapse. Why? Obviously has the tune initconf initialized the global variable __logger !

It's all about closures. http. Handlerfunc is actually a closed bag.

The logger used in the final HelloWorld is not the logger of the global variable, but the free variable in the closure.

Initconf () was not called when the closure was generated, so __logger it was nil, so the free variable logger in the closure was nil.