command: make the type a string, for easier equality test

pkg/command/command.go

@@ -16,14 +16,12 @@ var _ fmt.Stringer = (*Command)(nil)
 // by one or more slash-separated Segments of lowercase characters.
 //
 // [Command]: https://github.com/ucan-wg/spec#command
-type Command struct {
-	segments []string
-}
+type Command string
 
 // New creates a validated command from the provided list of segment strings.
 // An error is returned if an invalid Command would be formed
 func New(segments ...string) Command {
-	return Command{segments: segments}
+	return Top().Join(segments...)
 }
 
 // Parse verifies that the provided string contains the required
@@ -33,20 +31,20 @@ func New(segments ...string) Command {
 // [segment structure]: https://github.com/ucan-wg/spec#segment-structure
 func Parse(s string) (Command, error) {
 	if !strings.HasPrefix(s, "/") {
-		return Command{}, ErrRequiresLeadingSlash
+		return "", ErrRequiresLeadingSlash
 	}
 
 	if len(s) > 1 && strings.HasSuffix(s, "/") {
-		return Command{}, ErrDisallowsTrailingSlash
+		return "", ErrDisallowsTrailingSlash
 	}
 
 	if s != strings.ToLower(s) {
-		return Command{}, ErrRequiresLowercase
+		return "", ErrRequiresLowercase
 	}
 
 	// The leading slash will result in the first element from strings.Split
 	// being an empty string which is removed as strings.Join will ignore it.
-	return Command{strings.Split(s, "/")[1:]}, nil
+	return Command(s), nil
 }
 
 // MustParse is the same as Parse, but panic() if the parsing fail.
@@ -58,14 +56,14 @@ func MustParse(s string) Command {
 	return c
 }
 
-// [Top] is the most powerful capability.
+// Top is the most powerful capability.
 //
 // This function returns a Command that is a wildcard and therefore represents the
 // most powerful ability. As such, it should be handled with care and used sparingly.
 //
 // [Top]: https://github.com/ucan-wg/spec#-aka-top
 func Top() Command {
-	return New()
+	return Command(separator)
 }
 
 // IsValid returns true if the provided string is a valid UCAN command.
@@ -77,17 +75,34 @@ func IsValid(s string) bool {
 // Join appends segments to the end of this command using the required
 // segment separator.
 func (c Command) Join(segments ...string) Command {
-	return Command{append(c.segments, segments...)}
+	size := 0
+	for _, s := range segments {
+		size += len(s)
+	}
+	if size == 0 {
+		return c
+	}
+	buf := make([]byte, 0, len(c)+size+len(segments))
+	buf = append(buf, []byte(c)...)
+	for _, s := range segments {
+		if s != "" {
+			if len(buf) > 1 {
+				buf = append(buf, separator...)
+			}
+			buf = append(buf, []byte(s)...)
+		}
+	}
+	return Command(buf)
 }
 
 // Segments returns the ordered segments that comprise the Command as a
 // slice of strings.
 func (c Command) Segments() []string {
-	return c.segments
+	return strings.Split(string(c), separator)
 }
 
 // String returns the composed representation the command.  This is also
 // the required wire representation (before IPLD encoding occurs.)
 func (c Command) String() string {
-	return "/" + strings.Join(c.segments, "/")
+	return string(c)
 }