Added new static value character

You can use the '!' character to define static json as a path
component.

For example,

  {name.last,"foo":!"bar"} => {name.last,"foo":"bar"}

see #249

gjson.go

@@ -1807,7 +1807,7 @@ func isSimpleName(component string) bool {
 			return false
 		}
 		switch component[i] {
-		case '[', ']', '{', '}', '(', ')', '#', '|':
+		case '[', ']', '{', '}', '(', ')', '#', '|', '!':
 			return false
 		}
 	}
@@ -1871,23 +1871,25 @@ type parseContext struct {
 // use the Valid function first.
 func Get(json, path string) Result {
 	if len(path) > 1 {
-		if !DisableModifiers {
-			if path[0] == '@' {
-				// possible modifier
-				var ok bool
-				var npath string
-				var rjson string
+		if (path[0] == '@' && !DisableModifiers) || path[0] == '!' {
+			// possible modifier
+			var ok bool
+			var npath string
+			var rjson string
+			if path[0] == '@' && !DisableModifiers {
 				npath, rjson, ok = execModifier(json, path)
-				if ok {
-					path = npath
-					if len(path) > 0 && (path[0] == '|' || path[0] == '.') {
-						res := Get(rjson, path[1:])
-						res.Index = 0
-						res.Indexes = nil
-						return res
-					}
-					return Parse(rjson)
+			} else if path[0] == '!' {
+				npath, rjson, ok = execStatic(json, path)
+			}
+			if ok {
+				path = npath
+				if len(path) > 0 && (path[0] == '|' || path[0] == '.') {
+					res := Get(rjson, path[1:])
+					res.Index = 0
+					res.Indexes = nil
+					return res
 				}
+				return Parse(rjson)
 			}
 		}
 		if path[0] == '[' || path[0] == '{' {
@@ -2556,8 +2558,40 @@ func safeInt(f float64) (n int64, ok bool) {
 	return int64(f), true
 }
 
+// execStatic parses the path to find a static value.
+// The input expects that the path already starts with a '!'
+func execStatic(json, path string) (pathOut, res string, ok bool) {
+	name := path[1:]
+	if len(name) > 0 {
+		switch name[0] {
+		case '{', '[', '"', '+', '-', '0', '1', '2', '3', '4', '5', '6', '7',
+			'8', '9':
+			_, res = parseSquash(name, 0)
+			pathOut = name[len(res):]
+			return pathOut, res, true
+		}
+	}
+	for i := 1; i < len(path); i++ {
+		if path[i] == '|' {
+			pathOut = path[i:]
+			name = path[1:i]
+			break
+		}
+		if path[i] == '.' {
+			pathOut = path[i:]
+			name = path[1:i]
+			break
+		}
+	}
+	switch strings.ToLower(name) {
+	case "true", "false", "null", "nan", "inf":
+		return pathOut, name, true
+	}
+	return pathOut, res, false
+}
+
 // execModifier parses the path to find a matching modifier function.
-// then input expects that the path already starts with a '@'
+// The input expects that the path already starts with a '@'
 func execModifier(json, path string) (pathOut, res string, ok bool) {
 	name := path[1:]
 	var hasArgs bool

gjson_test.go

@@ -2410,3 +2410,31 @@ func TestQueryGetPath(t *testing.T) {
 		assert(t, arr[i].Path(readmeJSON) == fmt.Sprintf("friends.%d.first", i))
 	}
 }
+
+func TestStaticJSON(t *testing.T) {
+	json := `{
+		"name": {"first": "Tom", "last": "Anderson"}
+	}`
+	assert(t, Get(json,
+		`"bar"`).Raw ==
+		``)
+	assert(t, Get(json,
+		`!"bar"`).Raw ==
+		`"bar"`)
+	assert(t, Get(json,
+		`!{"name":{"first":"Tom"}}.{name.first}.first`).Raw ==
+		`"Tom"`)
+	assert(t, Get(json,
+		`{name.last,"foo":!"bar"}`).Raw ==
+		`{"last":"Anderson","foo":"bar"}`)
+	assert(t, Get(json,
+		`{name.last,"foo":!{"a":"b"},"that"}`).Raw ==
+		`{"last":"Anderson","foo":{"a":"b"}}`)
+	assert(t, Get(json,
+		`{name.last,"foo":!{"c":"d"},!"that"}`).Raw ==
+		`{"last":"Anderson","foo":{"c":"d"},"_":"that"}`)
+	assert(t, Get(json,
+		`[!true,!false,!null,!inf,!nan,!hello,{"name":!"andy",name.last},+inf,!["any","thing"]]`).Raw ==
+		`[true,false,null,inf,nan,{"name":"andy","last":"Anderson"},["any","thing"]]`,
+	)
+}