Like everything in existence, a generator is a function that (eventually) takes input and (eventually) returns output.
Setup
I will assume from this post on that
go mod inithave been executed (if not see 101).
terminal
touch main.go division.generator.go
main.go
package main
//go:generate go run division.generator.go 12 4
import "fmt"
func main() {}
NOTE: Adding the suffix
*.generator.goit's not part of the convention it's something I do.
division.go
//go:build ignore
package main
import (
"fmt"
"os"
"strconv"
)
func main() {
args := os.Args
invoker := os.Getenv("GOFILE") // injected since it is executed via go:generate
numerator, _ := strconv.Atoi(args[1])
denominator, _ := strconv.Atoi(args[2])
fmt.Println("args", args)
fmt.Println("invoker", invoker)
fmt.Printf("%d / %d = %d\n", numerator, denominator, numerator/denominator)
}
Usage
terminal
go generate ./...
output
args [path/to/exe/division.generator 12 4]
invoker main.go
12 / 4 = 3
A lot of env variables
GOFILE is not the only env variable provided.
for _, ev := range []string{"GOARCH", "GOOS", "GOFILE", "GOLINE", "GOPACKAGE", "DOLLAR"} {
fmt.Println(ev, os.Getenv(ev))
}
terminal
GOARCH arm64
GOOS darwin
GOFILE main.go
GOLINE 3 // lineno of //go:generate
GOPACKAGE main
DOLLAR $
Reuse across different projects
It is necessary to build the generator and place it in the GOPATH.
terminal
go build -o division division.generator.go
mv ./division $GOPATH/bin
main.go
package main
//go:generate division 12 4
import "fmt"
func main() {}
NOTE: No
go run, just the name of the executable.
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