use map to store optimizer hyperparams

Author: kexinzhao

src/function.h

@@ -219,7 +219,7 @@ class Adam {
   void Update(VariableHandle input) {
     PADDLE_ENFORCE(get_global_tape().HasBeenBackwarded(),
                    "optimization must happen after the backward");
-    auto hyperparams = input->MutableHyperParams();
+    auto *hyperparams = input->MutableHyperParams("adam");
     // initialize states if they haven't been created
     if (hyperparams->empty()) {
       framework::AttributeMap attrs;

src/variable.h

@@ -80,7 +80,13 @@ class Variable {
     return var_.GetMutable<T>();
   }
 
-  std::vector<VariableHandle>* MutableHyperParams() { return &hyperparams_; }
+  std::vector<VariableHandle>* MutableHyperParams(
+      const std::string& optimizer) {
+    PADDLE_ENFORCE(hyperparams_.find(optimizer) != hyperparams_.end(),
+                   "%s optimizer is not supported",
+                   optimizer);
+    return &hyperparams_[optimizer];
+  }
 
  private:
   int count() {
@@ -94,8 +100,9 @@ class Variable {
   // Not own
   std::weak_ptr<Variable> grad_;
 
-  // Adam Optimizer hyperparameter
-  std::vector<VariableHandle> hyperparams_;
+  // Optimizer hyperparameters
+  std::unordered_map<std::string, std::vector<VariableHandle>> hyperparams_{
+      {"adam", {}}};
 };
 
 }  // namespace tape