add support for description string

1 files changed, 15 insertions, 3 deletions

diff --git a/parse.go b/parse.go
index 26b530a..3cd00aa 100644
--- a/parse.go
+++ b/parse.go
@@ -67,9 +67,10 @@ type Config struct {
 
 // Parser represents a set of command line options with destination values
 type Parser struct {
-	spec    []*spec
-	config  Config
-	version string
+	spec        []*spec
+	config      Config
+	version     string
+	description string
 }
 
 // Versioned is the interface that the destination struct should implement to
@@ -80,6 +81,14 @@ type Versioned interface {
 	Version() string
 }
 
+// Described is the interface that the destination struct should implement to
+// make a description string appear at the top of the help message.
+type Described interface {
+	// Description returns the string that will be printed on a line by itself
+	// at the top of the help message.
+	Description() string
+}
+
 // walkFields calls a function for each field of a struct, recursively expanding struct fields.
 func walkFields(v reflect.Value, visit func(field reflect.StructField, val reflect.Value, owner reflect.Type) bool) {
 	t := v.Type()
@@ -102,6 +111,9 @@ func NewParser(config Config, dests ...interface{}) (*Parser, error) {
 		if dest, ok := dest.(Versioned); ok {
 			p.version = dest.Version()
 		}
+		if dest, ok := dest.(Described); ok {
+			p.description = dest.Description()
+		}
 		v := reflect.ValueOf(dest)
 		if v.Kind() != reflect.Ptr {
 			panic(fmt.Sprintf("%s is not a pointer (did you forget an ampersand?)", v.Type()))