text: #pragma once
  //------------------------------------------------------------------------------
  //
  //   Copyright 2018-2019 Fetch.AI Limited
  //
  //   Licensed under the Apache License, Version 2.0 (the "License");
  //   you may not use this file except in compliance with the License.
  //   You may obtain a copy of the License at
  //
  //       http://www.apache.org/licenses/LICENSE-2.0
  //
  //   Unless required by applicable law or agreed to in writing, software
  //   distributed under the License is distributed on an "AS IS" BASIS,
  //   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  //   See the License for the specific language governing permissions and
  //   limitations under the License.
  //
  //------------------------------------------------------------------------------
  
  #include "ml/ops/ops.hpp"
  
  namespace fetch {
  namespace ml {
  namespace ops {
  
  template <class T>
  class Criterion
  {
  public:
    using ArrayType    = T;
    using Datatype     = typename ArrayType::Type;
    using ArrayPtrType = std::shared_ptr<ArrayType>;
  
    Criterion()
    {}
  
    virtual typename ArrayType::Type Forward(std::vector<ArrayType> const &inputs)  = 0;
    virtual ArrayType                Backward(std::vector<ArrayType> const &inputs) = 0;
  };
  
  }  // namespace ops
  }  // namespace ml
  }  // namespace fetch
  