xtd::collections::generic::ienumerable< type_t > Class Template Reference

Inheritance diagram for xtd::collections::generic::ienumerable< type_t >:

Definition

template<class type_t>
class xtd::collections::generic::ienumerable< type_t >

Exposes the enumerator, which supports a simple iteration over a collection of a specified type.

Definition

template<class type_t>
class ienumerable interface_

Header

#include <xtd/collections/generic/ienumerable>

Namespace

xtd::collections::generic

Library

xtd.core

Examples

The following example demonstrates how to implement the xtd::collections::generic::ienumerable <type_t> interface. When you implement xtd::collections::generic::ienumerable <type_t>, you must also implement xtd::collections::generic::ienumerator <type_t>.

#include <xtd/xtd>
 
class program {
public:
  static auto main() -> void {
    test_stream_reader_enumerable();
    console::write_line("---");
    test_reading_file();
  }
  
  static void test_stream_reader_enumerable() {
    // Check the memory before the iterator is used.
    auto memory_before = memory_information::get_used_process_memory();
    auto strings_found = list<string> {};
    // Open a file with the stream_reader_enumerable and check for a string.
    try {
      for (auto line : stream_reader_enumerable {path::combine(path::get_temp_path(), "temp_file.txt")})
        if (line.contains("string to search for")) strings_found.add(line);
      console::write_line("Found: {}", strings_found.count());
    } catch (const file_not_found_exception&) {
      console::write_line("This example requires a file named {}.", path::combine(path::get_temp_path(), "temp_file.txt"));
      return;
    }
    
    // Check the memory after the iterator and output it to the console.
    auto memory_after = memory_information::get_used_process_memory();
    console::write_line("Memory Used With Iterator = \t{} kb", (memory_after - memory_before) / 1024);
  }
 
  static void test_reading_file() {
    size memory_before = memory_information::get_used_process_memory();
 
    auto file_contents = list<string> {};
    try {
      auto sr = stream_reader {path::combine(path::get_temp_path(), "temp_file.txt")};
      // Add the file contents to a generic list of strings.
      while (!sr.end_of_stream())
        file_contents.add(sr.read_line());
      sr.close();
    } catch (const file_not_found_exception&) {
      console::write_line("This example requires a file named {}.", path::combine(path::get_temp_path(), "temp_file.txt"));
      return;
    }
    
    // Check for the string.
    auto strings_found = list<string> {};
    for (auto line : file_contents)
      if (line.contains("string to search for")) strings_found.add(line);
    console::write_line("Found: {}", strings_found.count());
 
    // Check the memory after when the iterator is not used, and output it to the console.
    auto memory_after = memory_information::get_used_process_memory();
    console::write_line("Memory Used Without Iterator = \t{} kb", (memory_after - memory_before) / 1024);
  }
 
  // you must also implement xtd::collections::generic::ienumerable <type_t> and xtd::collections::generic::ienumerator <type_t>
  class stream_reader_enumerable : public ienumerable<string> {
  private:
    string file_path_;
    
  public:
    stream_reader_enumerable(const string& file_path) : file_path_ {file_path} {}
    
    // Must implement get_enumerator, which returns a new stream_reader_enumerator.
    enumerator<string> get_enumerator() const override {return {new_ptr<stream_reader_enumerator>(file_path_)};}
  };
  
  // When you implement xtd::collections::generic::ienumerable <type_t>, you must also implement xtd::collections::generic::ienumerator <type_t>, which will walk through the contents of the file one line at a time.
  class stream_reader_enumerator : public object, public ienumerator<string> {
  private:
    stream_reader sr_;
    std::optional<string> current_;
 
  public:
    stream_reader_enumerator(const string& file_path) : sr_ {file_path} {}
    ~stream_reader_enumerator() {sr_.close();}
 
    // Implement current, move_next and reset, which are required by ienumerator.
    const string& current() const override {
      if (!current_.has_value()) throw invalid_operation_exception {};
      return current_.value();
    }
        
    bool move_next() override {
      if (sr_.end_of_stream()) current_.reset();
      else current_ = sr_.read_line();
      return current_.has_value();
    }
    
    void reset() override {
      sr_.base_stream()->get().seekg(0, std::ios_base::beg);
      current_.reset();
    }
  };
};
 
startup_(program::main);
 
// This code produces the following output :
//
// Found: 2
// Memory Used With Iterator =   0 kb
// ---
// Found: 2
// Memory Used Without Iterator =   64 kb

Remarks

xtd::collections::generic::ienumerable <type_t> is the base interface for collections in the xtd::collections::generic namespace such as xtd::collections::generic::list <type_t>, xtd::collections::generic::dictionary <key_t, value_t>, and xtd::collections::generic::stack <type_t> and other generic collections such as xtd::collections::object_model::observable_collection <type_t> and xtd::collections::concurent::concurrent_stack <type_t>. Collections that implement xtd::collections::generic::ienumerable <type_t> can be enumerated by using the for each statement.

For the non-generic version of this interface, see xtd::collections::ienumerable.

xtd::collections::generic::ienumerable <type_t> contains a single method that you must implement when implementing this interface; xtd::collections::generic::ienumerable::get_enumerator, which returns an xtd::collections::generic::enumerator <type_t> object. The returned xtd::collections::generic::enumerator <type_t> provides the ability to iterate through the collection by exposing a xtd::collections::generic::enumerator::current property.

Public Aliases
using	value_type
	Represents the xtd::collections::generic::ienumerable value type.
using	iterator
	Represents the iterator of xtd::collections::generic::ienumerable value type.
using	const_iterator
	Represents the const iterator of xtd::collections::generic::ienumerable value type.

Public Methods
virtual auto	get_enumerator () const -> xtd::collections::generic::enumerator< type_t >=0
	Returns an enumerator that iterates through a collection.

Additional Inherited Members
using	iterator
	Represents the iterator of enumerable value type.
using	const_iterator
	Represents the const iterator of enumerable value type.
using	enumerable_type
	Represents the ienumerable enumerable type.
using	source_type
	Represents the ienumerable source type.
using	ienumerable
	Represents the ienumerable value type.
using	list
	Represents the list value type.
virtual auto	begin () const -> const_iterator
	Returns an iterator to the first element of the enumerable.
virtual auto	cbegin () const -> const_iterator
	Returns an iterator to the first element of the enumerable.
virtual auto	cend () const -> const_iterator
	Returns an iterator to the element following the last element of the enumerable.
virtual auto	end () const -> const_iterator
	Returns an iterator to the element following the last element of the enumerable.
auto	aggregate (const std::function< type_t(const type_t &, const type_t &)> &func) const -> type_t
	Applies an accumulator function over a sequence.
auto	all (const std::function< bool(const type_t &)> &predicate) const -> bool
	Determines whether all elements of a sequence satisfy a condition.
auto	any () const noexcept -> bool
	Determines whether a sequence contains any elements.
auto	append (const type_t &element) const noexcept
	Appends a value to the end of the sequence.
auto	as_enumerable () const noexcept
	Returns the input typed as xtd::collections::generic::ienumerable <type_t>.
auto	average () const noexcept
	Computes the average of a sequence of source_t values.
auto	cast () const noexcept
	Casts the elements of an xtd::collections::generic::ienumerable to the specified type.
auto	chunk (xtd::size size) const
	Splits the elements of a sequence into chunks of size at most size.
auto	concat (const ienumerable< type_t > &second) const noexcept
	Concatenates two sequences.
auto	contains (const type_t &value) const noexcept -> bool
	Determines whether a sequence contains a specified element by using the default equality comparer.
auto	count () const noexcept -> xtd::size
	Returns the number of elements in current sequence.
auto	count_by (const std::function< key_t(const type_t &)> &key_selector) const noexcept
	Returns the count of elements in the current sequence grouped by key.
auto	default_if_empty () const noexcept
	Returns the elements of the specified sequence or the type parameter's default value in a singleton collection if the current sequence is empty.
auto	distinct () const noexcept
	Returns distinct elements from a sequence by using the default equality comparer to compare values.
auto	first_or_default (const std::function< bool(const type_t &)> &predicate, const type_t &default_value) const noexcept -> type_t
	Returns the first element of the sequence that satisfies a condition, or a specified default value if no such element is found.
auto	order () const
	Sorts the elements of a sequence in ascending order.
auto	order_by (const std::function< type_t(const type_t &)> &key_selector) const
	Sorts the elements of a sequence in ascending order according to a key.
auto	order_by_descending (const std::function< key_t(const type_t &)> &key_selector) const
	Sorts the elements of a sequence in descending order according to a key.
auto	select (const std::function< result_t(const type_t &)> &selector) const
	Projects each element of a sequence into a new form.
auto	to_array () const noexcept -> xtd::array< type_t >
	Creates a xtd::array <type_t> from an xtd::collections::generic::ienumerable <type_t>.
auto	to_list () const noexcept -> xtd::collections::generic::list< type_t >
	Creates a xtd::collections::generic::list <type_t> from an xtd::collections::generic::ienumerable <type_t>.
auto	where (const std::function< bool(const type_t &)> &predicate) const
	Filters a sequence of values based on a predicate.
static auto	to_const_iterator (typename source_collection_t::const_iterator &value, const source_collection_t &source_collection, const target_collection_t &target_collection) noexcept -> typename target_collection_t::const_iterator
	Converts source iterator to target iterator.
static auto	to_iterator (typename source_collection_t::const_iterator &value, const source_collection_t &source_collection, const target_collection_t &target_collection) noexcept -> typename target_collection_t::const_iterator
	Converts source iterator to target iterator.

Member Typedef Documentation

value_type

template<class type_t>

using xtd::collections::generic::ienumerable< type_t >::value_type

Represents the xtd::collections::generic::ienumerable value type.

iterator

template<class type_t>

using xtd::collections::generic::ienumerable< type_t >::iterator

Represents the iterator of xtd::collections::generic::ienumerable value type.

const_iterator

template<class type_t>

using xtd::collections::generic::ienumerable< type_t >::const_iterator

Represents the const iterator of xtd::collections::generic::ienumerable value type.

Member Function Documentation

get_enumerator()

template<class type_t>

virtual auto xtd::collections::generic::ienumerable< type_t >::get_enumerator ( ) const -> xtd::collections::generic::enumerator< type_t >

nodiscardpure virtual

Returns an enumerator that iterates through a collection.

Returns

An xtd::collections::generic::enumerator object that can be used to iterate through the collection.

Implemented in xtd::basic_string< char_t, traits_t, allocator_t >, xtd::basic_string< char >, xtd::basic_string< xtd::char16 >, xtd::basic_string< xtd::char32 >, xtd::basic_string< xtd::char8 >, xtd::basic_string< xtd::wchar >, xtd::collections::generic::enumerable_generator< type_t >, and xtd::collections::generic::hash_set< type_t, hasher_t, equator_t, allocator_t >.

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The documentation for this class was generated from the following file:

• xtd.core/include/xtd/collections/generic/ienumerable.hpp