Poking at Exercise 2.2 on p. 44 of the Go Programming Language book and learning about Go Modules in the process.
This is a working Go Modules example that is outside the $GOPATH.
~/scripts/unit_conversion$ tree
.
├── go.mod
├── mainapp
│ └── main.go
└── unit_conversion
└── unit_conversion.go
2 directories, 3 files
Notice that the go.mod file is in the root/parent directory, and below that are both the mainapp/ dir and the unit_conversion dir, which houses the unit_conversion Go Package.
To create the go.mod file, this was run:
$ go mod init fake.com/unit_conversion
Notice that main.go is in it's own folder, a folder that is a sibling of the unit_conversion package. Also, note that there are no go.mod files in either mainapp/, nor unit_conversion/.
The import in main.go looks like this:
"fake.com/unit_conversion/unit_conversion"
To call functions / vars inside unit_conversion.go from main.go, we use the pacakge name then a dot then the variable / function name.
unit_conversion.FeetToMetersPretty(1)
https://medium.com/faun/golang-package-management-using-go-modules-d3c929900114
https://medium.com/@adiach3nko/package-management-with-go-modules-the-pragmatic-guide-c831b4eaaf31