Revert #128, update docs and add tests to Tokenizer.Remaining() (#129)

json/token.go

@@ -43,17 +43,6 @@ type Tokenizer struct {
 	// null, true, false, numbers, or quoted strings.
 	Value RawValue
 
-	// Position is the Tokenizer's current index into the underlying byte slice.
-	// Since the Tokenizer has already been advanced by calling Next, this
-	// position will be the first index of the next token.  The position of
-	// the current Value can be calculated by subtracting len(token.value).
-	// Accordingly, slicing the underlying bytes like:
-	//
-	//   b[token.Position-len(token.Value):token.Position]
-	//
-	// will yield the current Value.
-	Position int
-
 	// When the tokenizer has encountered invalid content this field is not nil.
 	Err error
 
@@ -102,7 +91,6 @@ func (t *Tokenizer) Reset(b []byte) {
 	// However, it does not compile down to an invocation of duff-copy.
 	t.Delim = 0
 	t.Value = nil
-	t.Position = 0
 	t.Err = nil
 	t.Depth = 0
 	t.Index = 0
@@ -139,16 +127,13 @@ skipLoop:
 
 	if i > 0 {
 		t.json = t.json[i:]
-		t.Position += i
 	}
 
 	if len(t.json) == 0 {
 		t.Reset(nil)
 		return false
 	}
 
-	lenBefore := len(t.json)
-
 	var kind Kind
 	switch t.json[0] {
 	case '"':
@@ -179,8 +164,6 @@ skipLoop:
 		t.Value, t.json, t.Err = t.json[:1], t.json[1:], syntaxError(t.json, "expected token but found '%c'", t.json[0])
 	}
 
-	t.Position += lenBefore - len(t.json)
-
 	t.Depth = t.depth()
 	t.Index = t.index()
 	t.flags = t.flags.withKind(kind)
@@ -319,6 +302,14 @@ func (t *Tokenizer) String() []byte {
 }
 
 // Remaining returns the number of bytes left to parse.
+//
+// The position of the tokenizer's current Value within the original byte slice
+// can be calculated like so:
+//
+//		end := len(b) - tok.Remaining()
+//		start := end - len(tok.Value)
+//
+// And slicing b[start:end] will yield the tokenizer's current Value.
 func (t *Tokenizer) Remaining() int {
 	return len(t.json)
 }

json/token_test.go

@@ -45,7 +45,8 @@ func tokenize(t *testing.T, b []byte) (tokens []token) {
 	tok := NewTokenizer(b)
 
 	for tok.Next() {
-		start, end := tok.Position-len(tok.Value), tok.Position
+		end := len(b) - tok.Remaining()
+		start := end - len(tok.Value)
 		if end > len(b) {
 			t.Fatalf("token position too far [%d:%d], len(b) is %d", start, end, len(b))
 		}