Transfer python assertion in PReLU to c++ (#6261)

* removed assertion for PReLU, need to put the assertion in c implementation

* added assertion in PReLU for parameter validation

* modifications based on review

* removed inheritance relation based on review

* formatted code

* moved a helper function to anonymous namespace

* format code
Co-authored-by: NYao Chi <later@usopp.net>
Co-authored-by: Noneflow-ci-bot <69100618+oneflow-ci-bot@users.noreply.github.com>

oneflow/core/functional/impl/activation_functor.cpp

@@ -61,11 +61,30 @@ class ReluGradFunctor : public BinaryFunctor {
   }
 };
 
-class PReluFunctor : public BinaryFunctor {
+namespace {
+Maybe<void> CheckPReLUParametersValid(const std::shared_ptr<Tensor>& x,
+                                      const std::shared_ptr<Tensor>& alpha) {
+  int num_params = alpha->dim(0);
+  CHECK_OR_RETURN(((num_params == 1) || (num_params == x->shape()->At(1))))
+      << "num_parameters in prelu must be 1 or " << x->shape()->At(1);
+  return Maybe<void>::Ok();
+}
+}  // namespace
+
+class PReluFunctor {
  public:
   PReluFunctor() {
     op_ = CHECK_JUST(one::OpBuilder("prelu").Input("x").Input("alpha").Output("y").Build());
   }
+
+  Maybe<Tensor> operator()(const std::shared_ptr<Tensor>& x,
+                           const std::shared_ptr<Tensor>& alpha) const {
+    JUST(CheckPReLUParametersValid(x, alpha));
+    return OpInterpUtil::Dispatch<Tensor>(*op_, {x, alpha});
+  }
+
+ private:
+  std::shared_ptr<OpExpr> op_;
 };
 
 class PReluGradFunctor {

python/oneflow/nn/modules/activation.py

@@ -92,9 +92,6 @@ class PReLU(Module):
         self.weight = flow.nn.Parameter(flow.Tensor(num_parameters).fill_(init))
 
     def forward(self, x):
-        assert (
-            self.num_parameters == 1 or self.num_parameters == x.shape[1]
-        ), f"num_parameters in prelu must be 1 or {x.shape[1]}"
         return flow._C.prelu(x, self.weight)