Use constant hiwire ids for singleton values

src/hiwire.c

 #include <emscripten.h>
 
+#include "hiwire.h"
+
+// Define special ids for singleton constants. These must be less than -1 to
+// avoid being reused for other values.
+#define HW_UNDEFINED -2
+#define HW_TRUE -3
+#define HW_FALSE -4
+#define HW_NULL -5
+
 EM_JS(void, hiwire_setup, (), {
+  // These ids must match the constants above, but we can't use them from JS
   var hiwire = { objects : {}, counter : 1 };
+  hiwire.objects[-2] = undefined;
+  hiwire.objects[-3] = true;
+  hiwire.objects[-4] = false;
+  hiwire.objects[-5] = null;
 
   Module.hiwire_new_value = function(jsval)
   {
@@ -19,12 +33,18 @@ EM_JS(void, hiwire_setup, (), {
 
   Module.hiwire_decref = function(idval)
   {
+    if (idval < 0) {
+      return;
+    }
     var objects = hiwire.objects;
     delete objects[idval];
   };
 });
 
 EM_JS(int, hiwire_incref, (int idval), {
+  if (idval < 0) {
+    return;
+  }
   return Module.hiwire_new_value(Module.hiwire_get_value(idval));
 });
 
@@ -76,15 +96,29 @@ EM_JS(int, hiwire_bytes, (int ptr, int len), {
   return Module.hiwire_new_value(bytes);
 });
 
-EM_JS(int, hiwire_undefined, (), {
-  return Module.hiwire_new_value(undefined);
-});
+int
+hiwire_undefined()
+{
+  return HW_UNDEFINED;
+}
 
-EM_JS(int, hiwire_null, (), { return Module.hiwire_new_value(null); });
+int
+hiwire_null()
+{
+  return HW_NULL;
+}
 
-EM_JS(int, hiwire_true, (), { return Module.hiwire_new_value(true); });
+int
+hiwire_true()
+{
+  return HW_TRUE;
+}
 
-EM_JS(int, hiwire_false, (), { return Module.hiwire_new_value(false); });
+int
+hiwire_false()
+{
+  return HW_FALSE;
+}
 
 EM_JS(void, hiwire_throw_error, (int idmsg), {
   var jsmsg = Module.hiwire_get_value(idmsg);
@@ -159,20 +193,20 @@ EM_JS(void, hiwire_delete_member_obj, (int idobj, int ididx), {
   delete jsobj[jsidx];
 });
 
-EM_JS(void, hiwire_call, (int idfunc, int idargs), {
+EM_JS(int, hiwire_call, (int idfunc, int idargs), {
   var jsfunc = Module.hiwire_get_value(idfunc);
   var jsargs = Module.hiwire_get_value(idargs);
   return Module.hiwire_new_value(jsfunc.apply(jsfunc, jsargs));
 });
 
-EM_JS(void, hiwire_call_member, (int idobj, int ptrname, int idargs), {
+EM_JS(int, hiwire_call_member, (int idobj, int ptrname, int idargs), {
   var jsobj = Module.hiwire_get_value(idobj);
   var jsname = UTF8ToString(ptrname);
   var jsargs = Module.hiwire_get_value(idargs);
   return Module.hiwire_new_value(jsobj[jsname].apply(jsobj, jsargs));
 });
 
-EM_JS(void, hiwire_new, (int idobj, int idargs), {
+EM_JS(int, hiwire_new, (int idobj, int idargs), {
   function newCall(Cls)
   {
     return new (Function.prototype.bind.apply(Cls, arguments));
@@ -219,7 +253,7 @@ EM_JS(int, hiwire_next, (int idobj), {
   // clang-format off
   if (jsobj.next === undefined) {
     // clang-format on
-    return -1;
+    return HW_ERROR;
   }
 
   return Module.hiwire_new_value(jsobj.next());

src/hiwire.h

@@ -14,6 +14,8 @@
  * object. There may be one or more keys pointing to the same object.
  */
 
+#define HW_ERROR -1
+
 /**
  * Initialize the variables and functions required for hiwire.
  */
@@ -359,7 +361,7 @@ hiwire_greater_than_equal(int ida, int idb);
 /**
  * Calls the `next` function on an iterator.
  *
- * Returns: -1 if `next` function is undefined.
+ * Returns: HW_ERROR if `next` function is undefined.
  */
 int
 hiwire_next(int idobj);

src/python2js.c

@@ -17,7 +17,7 @@ pythonexc2js()
   PyErr_Fetch(&type, &value, &traceback);
   PyErr_NormalizeException(&type, &value, &traceback);
 
-  int excval = -1;
+  int excval = HW_ERROR;
   int exc;
 
   if (type == NULL || type == Py_None || value == NULL || value == Py_None) {
@@ -86,7 +86,7 @@ exit:
 
   hiwire_throw_error(excval);
 
-  return -1;
+  return HW_ERROR;
 }
 
 static int
@@ -129,13 +129,13 @@ _python2js(PyObject* x, PyObject* map)
   } else if (PyLong_Check(x)) {
     long x_long = PyLong_AsLongLong(x);
     if (x_long == -1 && PyErr_Occurred()) {
-      return -1;
+      return HW_ERROR;
     }
     return hiwire_int(x_long);
   } else if (PyFloat_Check(x)) {
     double x_double = PyFloat_AsDouble(x);
     if (x_double == -1.0 && PyErr_Occurred()) {
-      return -1;
+      return HW_ERROR;
     }
     return hiwire_double(x_double);
   } else if (PyUnicode_Check(x)) {
@@ -151,13 +151,13 @@ _python2js(PyObject* x, PyObject* map)
         return hiwire_string_ucs4(data, length);
       default:
         PyErr_SetString(PyExc_ValueError, "Unknown Unicode KIND");
-        return -1;
+        return HW_ERROR;
     }
   } else if (PyBytes_Check(x)) {
     char* x_buff;
     Py_ssize_t length;
     if (PyBytes_AsStringAndSize(x, &x_buff, &length)) {
-      return -1;
+      return HW_ERROR;
     }
     return hiwire_bytes((int)(void*)x_buff, length);
   } else if (JsProxy_Check(x)) {
@@ -166,7 +166,7 @@ _python2js(PyObject* x, PyObject* map)
     int jsarray = hiwire_array();
     if (_python2js_add_to_cache(map, x, jsarray)) {
       hiwire_decref(jsarray);
-      return -1;
+      return HW_ERROR;
     }
     size_t length = PySequence_Size(x);
     for (size_t i = 0; i < length; ++i) {
@@ -181,11 +181,11 @@ _python2js(PyObject* x, PyObject* map)
         return pyproxy_new((int)x);
       }
       int jsitem = _python2js_cache(pyitem, map);
-      if (jsitem == -1) {
+      if (jsitem == HW_ERROR) {
         _python2js_remove_from_cache(map, x);
         Py_DECREF(pyitem);
         hiwire_decref(jsarray);
-        return -1;
+        return HW_ERROR;
       }
       Py_DECREF(pyitem);
       hiwire_push_array(jsarray, jsitem);
@@ -193,30 +193,30 @@ _python2js(PyObject* x, PyObject* map)
     }
     if (_python2js_remove_from_cache(map, x)) {
       hiwire_decref(jsarray);
-      return -1;
+      return HW_ERROR;
     }
     return jsarray;
   } else if (PyDict_Check(x)) {
     int jsdict = hiwire_object();
     if (_python2js_add_to_cache(map, x, jsdict)) {
       hiwire_decref(jsdict);
-      return -1;
+      return HW_ERROR;
     }
     PyObject *pykey, *pyval;
     Py_ssize_t pos = 0;
     while (PyDict_Next(x, &pos, &pykey, &pyval)) {
       int jskey = _python2js_cache(pykey, map);
-      if (jskey == -1) {
+      if (jskey == HW_ERROR) {
         _python2js_remove_from_cache(map, x);
         hiwire_decref(jsdict);
-        return -1;
+        return HW_ERROR;
       }
       int jsval = _python2js_cache(pyval, map);
-      if (jsval == -1) {
+      if (jsval == HW_ERROR) {
         _python2js_remove_from_cache(map, x);
         hiwire_decref(jskey);
         hiwire_decref(jsdict);
-        return -1;
+        return HW_ERROR;
       }
       hiwire_push_object_pair(jsdict, jskey, jsval);
       hiwire_decref(jskey);
@@ -224,7 +224,7 @@ _python2js(PyObject* x, PyObject* map)
     }
     if (_python2js_remove_from_cache(map, x)) {
       hiwire_decref(jsdict);
-      return -1;
+      return HW_ERROR;
     }
     return jsdict;
   } else {
@@ -254,7 +254,7 @@ _python2js_add_to_cache(PyObject* map, PyObject* pyparent, int jsparent)
   if (PyDict_SetItem(map, pyparentid, jsparentid)) {
     Py_DECREF(pyparentid);
     Py_DECREF(jsparentid);
-    return -1;
+    return HW_ERROR;
   }
   Py_DECREF(pyparentid);
   Py_DECREF(jsparentid);
@@ -266,7 +266,7 @@ _python2js_remove_from_cache(PyObject* map, PyObject* pyparent)
 {
   PyObject* pyparentid = PyLong_FromSize_t((size_t)pyparent);
   if (PyDict_DelItem(map, pyparentid)) {
-    return -1;
+    return HW_ERROR;
   }
   Py_DECREF(pyparentid);
   return 0;
@@ -280,7 +280,7 @@ _python2js_cache(PyObject* x, PyObject* map)
   int result;
   if (val) {
     result = PyLong_AsLong(val);
-    if (result != -1) {
+    if (result != HW_ERROR) {
       result = hiwire_incref(result);
     }
     Py_DECREF(val);
@@ -298,7 +298,7 @@ python2js(PyObject* x)
   int result = _python2js_cache(x, map);
   Py_DECREF(map);
 
-  if (result == -1) {
+  if (result == HW_ERROR) {
     return pythonexc2js();
   }