func Whenf(cond bool, m string, args ...interface{}) Composer {
	return &condComposer{cond: cond, msg: NewFormatted(m, args...)}
}
Whenf returns a conditional message that is only logged if the
condition is bool, and creates a sprintf-style message, which will
itself only log if the base expression is not the empty string.
package message
import (
	"github.com/mongodb/grip/level"
)
type condComposer struct {
	cond bool
	msg  Composer
}
func When(cond bool, m interface{}) Composer {
	return &condComposer{cond: cond, msg: ConvertToComposer(level.Priority(0), m)}
}