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modulegopackageintrospection

Can I introspect the name of the main.main package?

This is a fairly niche problem, but I'm currently trying to write a conventions-based settings storage library with golang. It would be a great API boon if I could programmatically determine the running package name that wants to store something (eg "github.net/author/projectname/pkg") calling my library function.

With Python a similar thing could be achieved with the inspect module, or even with __main__.__file__ and a look at the file system.

Solution

  • You can get similar information if you use the following functions:

    The code may look like this:

    pc, file, line, ok := runtime.Caller(1)
if !ok { /*failed*/ }
println(pc, file, line, ok)

f := runtime.FuncForPC(pc)
if f == nil { /*failed*/ }
println(f.Name())

    If I put the above code (with the 1st line changed into runtime.Caller(0)) into a (randomly chosen) Go library which I have installed in GOROOT, it prints:

    134626026 /tmp/go-build223663414/github.com/mattn/go-gtk/gtk/_obj/gtk.cgo1.go -4585 true
github.com/mattn/go-gtk/gtk.Init

    Or it prints:

    134515752 /home/user/go/src/github.com/mattn/go-gtk/example/event/event.go 12 true
main.main

    The filename on the 1st line, and the 2nd line, seem to contain the information you are looking for.

    There are two problems:

    • It may give incorrect result if functions are automatically inlined by the compiler

    • For any function F defined in package main, the function name is just main.F. For example, if runtime.Caller(0) is called from main(), the function name is main.main even if the main() function is defined in a Go file found in GOROOT/src/github.com/mattn/go-gtk/.... In this case, the output from runtime.Caller is more useful than the output from runtime.FuncForPC.