1 files changed, 26 insertions, 0 deletions
diff --git a/cmd/jp/flag.go b/cmd/jp/flag.go
new file mode 100644
index 0000000..533b35d
--- /dev/null
+++ b/cmd/jp/flag.go
@@ -0,0 +1,26 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+type enumVar struct {
+	Choices []string // The acceptable choices the user may pass to the flag
+	Value   string   // the current value of the flag
+}
+
+// Set implements the flag.Value interface.
+func (so *enumVar) Set(v string) error {
+	for _, c := range so.Choices {
+		if c == v {
+			so.Value = v
+			return nil
+		}
+	}
+	return fmt.Errorf("invalid choice; must be one of %s", strings.Join(so.Choices, ","))
+}
+
+func (so *enumVar) String() string {
+	return so.Value
+}