assert in Go

assert.go

package main

import (
	"fmt"
	"os"
	"runtime"
)

func main() {
	foo(0)
	foo(1)
}

func foo(i int) {
	_ = "blah"
	assert(i == 0, "i must be zero")
	_ = 1 + 2
}

func assert(cond bool, reason string) {
	pc, file, line, ok := runtime.Caller(1)
	if !ok && !cond {
		// ???
		panic(reason)
	}
	if !cond {
		var fnName string
		fn := runtime.FuncForPC(pc)
		if fn != nil {
			fnName = fn.Name()
		}
		if fnName != "" {
			fmt.Fprintf(os.Stderr, "assert: %s:%d: %s: assertion failed: %s\n", file, line, fnName, reason)
		} else {
			fmt.Fprintf(os.Stderr, "assert: %s:%d: assertion failed: %s\n", file, line, reason)
		}
		os.Exit(1)
	}
}

example_output.txt

$ go run assert.go
assert: /tmp/assert.go:16: main.foo: assertion failed: i must be zero
exit status 1