Clarify (the existence of) the constant empty String

Takayuki 'January June' Suwa · Takayuki 'January June' Suwa · commit 933511540f2d · 2018-12-24T08:08:47.000+09:00
instead of use of naked global symbol.
diff --git a/cores/esp8266/AddrList.h b/cores/esp8266/AddrList.h
@@ -123,7 +123,7 @@ struct netifWrapper
 
     // common to all addresses of this interface
     String ifname () const          { return String(_netif->name[0]) + _netif->name[1]; }
-    const char* ifhostname () const { return _netif->hostname?: emptyString.c_str(); }
+    const char* ifhostname () const { return _netif->hostname?: String::empty().c_str(); }
     const char* ifmac () const      { return (const char*)_netif->hwaddr; }
     int ifnumber () const           { return _netif->num; }
 
diff --git a/cores/esp8266/WString.h b/cores/esp8266/WString.h
@@ -70,6 +70,13 @@ class String {
         explicit String(double, unsigned char decimalPlaces = 2);
         ~String(void);
 
+        // empty string singleton
+        // return the reference to the constant empty string.
+        static inline const String &empty() {
+            extern const String emptyString;
+            return emptyString;
+        }
+
         // memory management
         // return true on success, false on failure (in which case, the string
         // is left unchanged).  reserve(0), if successful, will validate an
@@ -294,7 +301,8 @@ class StringSumHelper: public String {
         }
 };
 
-extern const String emptyString;
+// only for backward compatibility
+extern const String emptyString __attribute__((deprecated("Use String::empty() instead.")));
 
 #endif  // __cplusplus
 #endif  // String_class_h
diff --git a/libraries/ESP8266HTTPUpdateServer/src/ESP8266HTTPUpdateServer.cpp b/libraries/ESP8266HTTPUpdateServer/src/ESP8266HTTPUpdateServer.cpp
@@ -20,8 +20,8 @@ ESP8266HTTPUpdateServer::ESP8266HTTPUpdateServer(bool serial_debug)
 {
   _serial_output = serial_debug;
   _server = NULL;
-  _username = emptyString;
-  _password = emptyString;
+  _username = String::empty();
+  _password = String::empty();
   _authenticated = false;
 }
 
@@ -33,7 +33,7 @@ void ESP8266HTTPUpdateServer::setup(ESP8266WebServer *server, const String& path
 
     // handler for the /update form page
     _server->on(path.c_str(), HTTP_GET, [&](){
-      if(_username != emptyString && _password != emptyString && !_server->authenticate(_username.c_str(), _password.c_str()))
+      if(_username != String::empty() && _password != String::empty() && !_server->authenticate(_username.c_str(), _password.c_str()))
         return _server->requestAuthentication();
       _server->send_P(200, PSTR("text/html"), serverIndex);
     });
@@ -61,7 +61,7 @@ void ESP8266HTTPUpdateServer::setup(ESP8266WebServer *server, const String& path
         if (_serial_output)
           Serial.setDebugOutput(true);
 
-        _authenticated = (_username == emptyString || _password == emptyString || _server->authenticate(_username.c_str(), _password.c_str()));
+        _authenticated = (_username == String::empty() || _password == String::empty() || _server->authenticate(_username.c_str(), _password.c_str()));
         if(!_authenticated){
           if (_serial_output)
             Serial.printf("Unauthenticated Update\n");
diff --git a/libraries/ESP8266HTTPUpdateServer/src/ESP8266HTTPUpdateServer.h b/libraries/ESP8266HTTPUpdateServer/src/ESP8266HTTPUpdateServer.h
@@ -10,12 +10,12 @@ class ESP8266HTTPUpdateServer
 
     void setup(ESP8266WebServer *server)
     {
-      setup(server, emptyString, emptyString);
+      setup(server, String::empty(), String::empty());
     }
 
     void setup(ESP8266WebServer *server, const String& path)
     {
-      setup(server, path, emptyString, emptyString);
+      setup(server, path, String::empty(), String::empty());
     }
 
     void setup(ESP8266WebServer *server, const String& username, const String& password)
diff --git a/libraries/ESP8266WebServer/src/ESP8266WebServer.cpp b/libraries/ESP8266WebServer/src/ESP8266WebServer.cpp
@@ -108,7 +108,7 @@ void ESP8266WebServer::begin(uint16_t port) {
 String ESP8266WebServer::_extractParam(String& authReq,const String& param,const char delimit) const {
   int _begin = authReq.indexOf(param);
   if (_begin == -1)
-    return emptyString;
+    return String::empty();
   return authReq.substring(_begin+param.length(),authReq.indexOf(delimit,_begin+param.length()));
 }
 
@@ -486,7 +486,7 @@ void ESP8266WebServer::_streamFileCore(const size_t fileSize, const String & fil
       contentType != String(FPSTR(mimeTable[none].mimeType))) {
     sendHeader(F("Content-Encoding"), F("gzip"));
   }
-  send(200, contentType, emptyString);
+  send(200, contentType, String::empty());
 }
 
 
@@ -499,19 +499,19 @@ const String& ESP8266WebServer::arg(String name) const {
     if ( _currentArgs[i].key == name )
       return _currentArgs[i].value;
   }
-  return emptyString;
+  return String::empty();
 }
 
 const String& ESP8266WebServer::arg(int i) const {
   if (i >= 0 && i < _currentArgCount)
     return _currentArgs[i].value;
-  return emptyString;
+  return String::empty();
 }
 
 const String& ESP8266WebServer::argName(int i) const {
   if (i >= 0 && i < _currentArgCount)
     return _currentArgs[i].key;
-  return emptyString;
+  return String::empty();
 }
 
 int ESP8266WebServer::args() const {
@@ -536,7 +536,7 @@ const String& ESP8266WebServer::header(String name) const {
     if (_currentHeaders[i].key.equalsIgnoreCase(name))
       return _currentHeaders[i].value;
   }
-  return emptyString;
+  return String::empty();
 }
 
 void ESP8266WebServer::collectHeaders(const char* headerKeys[], const size_t headerKeysCount) {
@@ -553,13 +553,13 @@ void ESP8266WebServer::collectHeaders(const char* headerKeys[], const size_t hea
 const String& ESP8266WebServer::header(int i) const {
   if (i < _headerKeysCount)
     return _currentHeaders[i].value;
-  return emptyString;
+  return String::empty();
 }
 
 const String& ESP8266WebServer::headerName(int i) const {
   if (i < _headerKeysCount)
     return _currentHeaders[i].key;
-  return emptyString;
+  return String::empty();
 }
 
 int ESP8266WebServer::headers() const {
@@ -619,7 +619,7 @@ void ESP8266WebServer::_handleRequest() {
 
 void ESP8266WebServer::_finalizeResponse() {
   if (_chunked) {
-    sendContent(emptyString);
+    sendContent(String::empty());
   }
 }
 
diff --git a/libraries/ESP8266WiFi/examples/IPv6/IPv6.ino b/libraries/ESP8266WiFi/examples/IPv6/IPv6.ino
@@ -98,7 +98,7 @@ void setup() {
   Serial.println();
   Serial.println(ESP.getFullVersion());
 
-  Serial.printf("IPV6 is%s enabled\n", LWIP_IPV6 ? emptyString.c_str() : " NOT");
+  Serial.printf("IPV6 is%s enabled\n", LWIP_IPV6 ? String::empty().c_str() : " NOT");
 
   WiFi.mode(WIFI_STA);
   WiFi.begin(STASSID, STAPSK);
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiAP.h b/libraries/ESP8266WiFi/src/ESP8266WiFiAP.h
@@ -37,7 +37,7 @@ class ESP8266WiFiAPClass {
     public:
 
         bool softAP(const char* ssid, const char* passphrase = NULL, int channel = 1, int ssid_hidden = 0, int max_connection = 4);
-        bool softAP(const String& ssid,const String& passphrase = emptyString,int channel = 1,int ssid_hidden = 0,int max_connection = 4);
+        bool softAP(const String& ssid,const String& passphrase = String::empty(),int channel = 1,int ssid_hidden = 0,int max_connection = 4);
         bool softAPConfig(IPAddress local_ip, IPAddress gateway, IPAddress subnet);
         bool softAPdisconnect(bool wifioff = false);
 
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.h b/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.h
@@ -38,7 +38,7 @@ class ESP8266WiFiSTAClass {
 
         wl_status_t begin(const char* ssid, const char *passphrase = NULL, int32_t channel = 0, const uint8_t* bssid = NULL, bool connect = true);
         wl_status_t begin(char* ssid, char *passphrase = NULL, int32_t channel = 0, const uint8_t* bssid = NULL, bool connect = true);
-        wl_status_t begin(const String& ssid, const String& passphrase = emptyString, int32_t channel = 0, const uint8_t* bssid = NULL, bool connect = true);
+        wl_status_t begin(const String& ssid, const String& passphrase = String::empty(), int32_t channel = 0, const uint8_t* bssid = NULL, bool connect = true);
         wl_status_t begin();
 
         //The argument order for ESP is not the same as for Arduino. However, there is compatibility code under the hood 

Original file line number	Diff line number	Diff line change
`@@ -10,12 +10,12 @@ class ESP8266HTTPUpdateServer`
`10`	`10`
`11`	`11`	`void setup(ESP8266WebServer *server)`
`12`	`12`	`{`
`13`		`- setup(server, emptyString, emptyString);`
	`13`	`+ setup(server, String::empty(), String::empty());`
`14`	`14`	`}`
`15`	`15`
`16`	`16`	`void setup(ESP8266WebServer *server, const String& path)`
`17`	`17`	`{`
`18`		`- setup(server, path, emptyString, emptyString);`
	`18`	`+ setup(server, path, String::empty(), String::empty());`
`19`	`19`	`}`
`20`	`20`
`21`	`21`	`void setup(ESP8266WebServer *server, const String& username, const String& password)`
Original file line number	Diff line number	Diff line change
`@@ -108,7 +108,7 @@ void ESP8266WebServer::begin(uint16_t port) {`
`108`	`108`	`String ESP8266WebServer::_extractParam(String& authReq,const String& param,const char delimit) const {`
`109`	`109`	`int _begin = authReq.indexOf(param);`
`110`	`110`	`if (_begin == -1)`
`111`		`- return emptyString;`
	`111`	`+ return String::empty();`
`112`	`112`	`return authReq.substring(_begin+param.length(),authReq.indexOf(delimit,_begin+param.length()));`
`113`	`113`	`}`
`114`	`114`
`@@ -486,7 +486,7 @@ void ESP8266WebServer::_streamFileCore(const size_t fileSize, const String & fil`
`486`	`486`	`contentType != String(FPSTR(mimeTable[none].mimeType))) {`
`487`	`487`	`sendHeader(F("Content-Encoding"), F("gzip"));`
`488`	`488`	`}`
`489`		`- send(200, contentType, emptyString);`
	`489`	`+ send(200, contentType, String::empty());`
`490`	`490`	`}`
`491`	`491`
`492`	`492`
`@@ -499,19 +499,19 @@ const String& ESP8266WebServer::arg(String name) const {`
`499`	`499`	`if ( _currentArgs[i].key == name )`
`500`	`500`	`return _currentArgs[i].value;`
`501`	`501`	`}`
`502`		`- return emptyString;`
	`502`	`+ return String::empty();`
`503`	`503`	`}`
`504`	`504`
`505`	`505`	`const String& ESP8266WebServer::arg(int i) const {`
`506`	`506`	`if (i >= 0 && i < _currentArgCount)`
`507`	`507`	`return _currentArgs[i].value;`
`508`		`- return emptyString;`
	`508`	`+ return String::empty();`
`509`	`509`	`}`
`510`	`510`
`511`	`511`	`const String& ESP8266WebServer::argName(int i) const {`
`512`	`512`	`if (i >= 0 && i < _currentArgCount)`
`513`	`513`	`return _currentArgs[i].key;`
`514`		`- return emptyString;`
	`514`	`+ return String::empty();`
`515`	`515`	`}`
`516`	`516`
`517`	`517`	`int ESP8266WebServer::args() const {`
`@@ -536,7 +536,7 @@ const String& ESP8266WebServer::header(String name) const {`
`536`	`536`	`if (_currentHeaders[i].key.equalsIgnoreCase(name))`
`537`	`537`	`return _currentHeaders[i].value;`
`538`	`538`	`}`
`539`		`- return emptyString;`
	`539`	`+ return String::empty();`
`540`	`540`	`}`
`541`	`541`
`542`	`542`	`void ESP8266WebServer::collectHeaders(const char* headerKeys[], const size_t headerKeysCount) {`
`@@ -553,13 +553,13 @@ void ESP8266WebServer::collectHeaders(const char* headerKeys[], const size_t hea`
`553`	`553`	`const String& ESP8266WebServer::header(int i) const {`
`554`	`554`	`if (i < _headerKeysCount)`
`555`	`555`	`return _currentHeaders[i].value;`
`556`		`- return emptyString;`
	`556`	`+ return String::empty();`
`557`	`557`	`}`
`558`	`558`
`559`	`559`	`const String& ESP8266WebServer::headerName(int i) const {`
`560`	`560`	`if (i < _headerKeysCount)`
`561`	`561`	`return _currentHeaders[i].key;`
`562`		`- return emptyString;`
	`562`	`+ return String::empty();`
`563`	`563`	`}`
`564`	`564`
`565`	`565`	`int ESP8266WebServer::headers() const {`
`@@ -619,7 +619,7 @@ void ESP8266WebServer::_handleRequest() {`
`619`	`619`
`620`	`620`	`void ESP8266WebServer::_finalizeResponse() {`
`621`	`621`	`if (_chunked) {`
`622`		`- sendContent(emptyString);`
	`622`	`+ sendContent(String::empty());`
`623`	`623`	`}`
`624`	`624`	`}`
`625`	`625`