ienumerable

using xtd::collections::ienumerable = typedef generic::ienumerable<xtd::any_object>

Exposes an enumerator, which supports a simple iteration over a non-generic collection.

using ienumerable = xtd::collections::generic::ienumerable<xtd::any_object>

Header

#include <xtd/collections/ienumerable>

Namespace

xtd::collections

Library

xtd.core

Examples

The following code example demonstrates the best practice for iterating a custom collection by implementing the xtd::collection::ienumerable and xtd::collection::ienumerator interfaces. In this example, members of these interfaces are not explicitly called, but they are implemented to support the use of for each to iterate through the collection. This example is a complete Console app.

#include <xtd/collections/array_list>
#include <xtd/console>
#include <xtd/startup>
 
using namespace xtd;
using namespace xtd::collections;
 
class program {
public:
  // Simple business object.
  struct person : public object, public iequatable<person>, public icomparable<person> {
  public:
    person(const string& first_name, const string last_name) : first_name {first_name}, last_name {last_name} {}
    
    string first_name;
    string last_name;
 
    int32 compare_to(const person& o) const noexcept override {
      if (first_name == o.first_name && last_name == o.last_name) return 0;
      if (first_name > o.first_name || (first_name == o.first_name && last_name > o.last_name)) return 1;
      return -1;
    }
    bool equals(const object& o) const noexcept override {return is<person>(o) && equals(as<person>(o));}
    bool equals(const person& o) const noexcept override {return compare_to(o) == 0;}
    string to_string() const noexcept override {return string::format("{} {}", first_name, last_name);}
  };
  
  // Collection of person objects. This class implements xtd::collections::ienumerable so that it can be used with for each syntax.
  class people : public ienumerable {
  private:
    array_list people_;
    
  public:
    people(const array<person>& p_array) {
      people_ = array_list(p_array.size());
      
      for (auto i = 0_z; i < p_array.size(); ++i)
        people_[i] = p_array[i];
    }
    
    // Implementation for the xtd::collections::ienumerable::get_enumerator method.
    enumerator get_enumerator() const override {
      return enumerator {new_ptr<people_enumerator>(people_)};
    }
  };
  
  // When you implement xtd::collections::ienumerable, you must also implement xtd::collections::ienumerator.
  class people_enumerator : public ienumerator {
  private:
    const array_list& people_;
 
    // Enumerators are positioned before the first element until the first xtd::collections::ienumerator::move_next() call.
    size position = array_list::npos;
    
  public:
    people_enumerator(const array_list& list) : people_(list) {}
    
    bool move_next() override {return ++position < people_.count();}
    
    void reset() override {position = array_list::npos;}
    
    const any_object& current() const override {
      if (position >= people_.size()) throw invalid_operation_exception {csf_};
      return people_[position];
    }
  };
 
  static auto main() -> void {
    auto people_array = xtd::array<person> {
      person {"John", "Smith"},
      person {"Jim", "Johnson"},
      person {"Sue", "Rabon"},
    };
    
    auto people_list = people {people_array};
    for (auto person : people_list)
      console::write_line(person);
  }
};
 
startup_(program::main);
 
 
// This code produces the following output :
//
// John Smith
// Jim Johnson
// Sue Rabon

Remarks

xtd::collections::ienumerable is the base interface for all non-generic collections that can be enumerated. For the generic version of this interface see xtd::collections::generic::ieumerable <type_t>. xtd::collections::ienumerable contains a single method, xtd::collections::ienumerable::get_enumerator, which returns an xtd::collections::ienumerator. xtd::collections::ienumerator provides the ability to iterate through the collection by exposing a xtd::collections::ienumerator::current property and xtd::collections::ienumerator::move_next and xtd::collections::ienumeraror::reset methods.

It is a best practice to implement xtd::collections::ienumerable and xtd::collections::ienumerator on your collection classes to enable the for each syntax, however implementing xtd::collections::ienumerable is not required. If your collection does not implement xtd::collections::ienumerable, you must still follow the iterator pattern to support this syntax by providing a xtd::collections::ienumerable::get_enumerator method that returns an interface, class or struct. You must provide a class that contains a xtd::collections::ienumerator::current property, and xtd::collections::ienumerator::move_next and Reset methods as described by xtd::collections::ienumerator, but the class does not have to implement xtd::collections::ienumerator.