While working on Node refactoring leading up to CL 7360, I found myself applying 8 different templates (one per relevant field) sequentially. It would be nicer to use--and I think faster to execute--to apply them all in a single pass.

The template could look like a sequence of alternating pairs of before and after:

package P

func before(s string) error { return fmt.Errorf("%s", s) }
func after(s string)  error { return errors.New(s) }

func before(msg string) { log.Fatalf("%s", msg) }
func after(msg string)  { log.Fatal(msg) }

The semantics would be that the output would be equivalent to applying each of the pairs sequentially as a template.

Thoughts? I'm happy to help with implementation.