ident: member interface

For representing full identifiers of system and member.

Signed-off-by: Yonah <contrib@gensokyo.uk>

ident/ident.go

@@ -3,7 +3,9 @@
 package ident
 
 import (
+	"encoding"
 	"errors"
+	"fmt"
 	"strconv"
 )
 
@@ -21,3 +23,21 @@ func (e *UnexpectedSizeError) Error() string {
 	return "got " + strconv.Itoa(len(e.Data)) + " bytes for " +
 		"a " + strconv.Itoa(e.Want) + "-byte identifier"
 }
+
+// MS is a system or member identifier.
+type MS interface {
+	encoding.TextMarshaler
+	encoding.TextUnmarshaler
+	fmt.Stringer
+
+	// EncodedSize returns the number of bytes appended by Encode.
+	EncodedSize() int
+	// Encode appends the canonical string representation of MS to dst and
+	// returns the extended buffer.
+	Encode(dst []byte) []byte
+
+	// ident is a no-op function but serves to distinguish types that are
+	// identifiers from ordinary types with custom marshaler/unmarshaler
+	// behaviour: a type is an identifier part if it has an ident method.
+	ident()
+}

ident/ident_test.go

@@ -69,7 +69,7 @@ func (testCases rTestCases[V, S]) run(t *testing.T) {
 				}
 
 				if got := S(&tc.ident).String(); got != string(tc.want) {
-					t.Errorf("String: %#v, want %#v", []byte(got), tc.want)
+					t.Errorf("String: %s, want %s", got, tc.want)
 				}
 			})
 		})

ident/member.go

@@ -23,6 +23,8 @@ type M struct {
 	System S
 }
 
+func (*M) ident() {}
+
 const (
 	// SizeMember is the size of the binary representation of [M].
 	SizeMember = SizeSystem * 2
@@ -30,6 +32,9 @@ const (
 	EncodedSizeMember = SizeMember / 3 * 4
 )
 
+// EncodedSize returns the number of bytes appended by Encode.
+func (*M) EncodedSize() int { return EncodedSizeMember }
+
 // Encode appends the canonical string representation of mid to dst and returns
 // the extended buffer.
 func (mid *M) Encode(dst []byte) []byte {

ident/system.go

@@ -31,6 +31,8 @@ type S struct {
 	ID uint64
 }
 
+func (*S) ident() {}
+
 const (
 	// SizeSystem is the size of the binary representation of [S].
 	SizeSystem = 24
@@ -38,6 +40,9 @@ const (
 	EncodedSizeSystem = SizeSystem / 3 * 4
 )
 
+// EncodedSize returns the number of bytes appended by Encode.
+func (*S) EncodedSize() int { return EncodedSizeSystem }
+
 // Encode appends the canonical string representation of sid to dst and returns
 // the extended buffer.
 func (sid *S) Encode(dst []byte) []byte {