add set global field (#177)

include/dmlc/lua.h

@@ -210,6 +210,12 @@ class LuaState {
    * \return The global field value.
    */
   inline LuaRef operator[](const std::string& key);
+  /*!
+   * \brief Set the value to the global table.
+   * \param key The key of the global field.
+   * \param value The value to the set.
+   */
+  inline void SetGlobalField(const std::string& key, const LuaRef& value);
   /*!
    *  Get a thread local version of lua state.
    *  The LuaState runs in thread local mode,
@@ -544,6 +550,14 @@ inline LuaRef LuaState::operator[](const std::string& key) {
   return ret;
 }
 
+inline void LuaState::SetGlobalField(
+    const std::string& key, const LuaRef& value) {
+  this->PRun_([this, &key, &value](lua_State* L) {
+      lua_rawgeti(L, LUA_REGISTRYINDEX, value.ref_);
+      lua_setglobal(L, key.c_str());
+    });
+}
+
 inline LuaRef::LuaRef(const LuaRef& other) {
   if (other.state_ != nullptr) {
     state_ = other.state_;