text: /*
   * Copyright 2015-present Facebook, Inc.
   *
   * 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.
   */
  
  #pragma once
  
  #include <cstddef>
  #include <type_traits>
  
  namespace folly { namespace detail {
  
  // Shortcut, so we don't have to use enable_if everywhere
  struct FormatTraitsBase {
    typedef void enabled;
  };
  
  // Traits that define enabled, value_type, and at() for anything
  // indexable with integral keys: pointers, arrays, vectors, and maps
  // with integral keys
  template <class T, class Enable = void> struct IndexableTraits;
  
  // Base class for sequences (vectors, deques)
  template <class C>
  struct IndexableTraitsSeq : public FormatTraitsBase {
    typedef C container_type;
    typedef typename C::value_type value_type;
  
    static const value_type& at(const C& c, int idx) {
      return c.at(idx);
    }
  
    static const value_type& at(const C& c, int idx, const value_type& dflt) {
      return (idx >= 0 && size_t(idx) < c.size()) ? c.at(idx) : dflt;
    }
  };
  
  // Base class for associative types (maps)
  template <class C>
  struct IndexableTraitsAssoc : public FormatTraitsBase {
    typedef typename C::value_type::second_type value_type;
  
    static const value_type& at(const C& c, int idx) {
      return c.at(static_cast<typename C::key_type>(idx));
    }
  
    static const value_type& at(const C& c, int idx, const value_type& dflt) {
      auto pos = c.find(static_cast<typename C::key_type>(idx));
      return pos != c.end() ? pos->second : dflt;
    }
  };
  
  } // namespace detail
  } // namespace folly
  