xtd::hash_code Class Reference

Inheritance diagram for xtd::hash_code:

Definition

Combines the hash code for multiple values into a single hash code.

class hash_code : public xtd::object

Namespace

xtd

Library

xtd.core

Examples

The static methods in this class combine the default hash codes of several values.

#include <xtd/xtd>
 
using namespace xtd;
using namespace xtd::collections::generic;
 
struct order_order_line : public object, public iequatable<order_order_line> {
public:
  order_order_line(int order_id, int order_line_id) : order_id_ {order_id}, order_line_id_ {order_line_id} {}
  
  int order_id() const noexcept {return order_id_;}
  int order_line_id() const noexcept {return order_line_id_;}
  
  bool equals(const object& obj) const noexcept override {return is<order_order_line>(obj) && equals(as<order_order_line>(obj));}
  bool equals(const order_order_line& other) const noexcept override {return order_id_ == other.order_id_ && order_line_id_ == other.order_line_id_;}
  
  size get_hash_code() const noexcept override {return hash_code::combine(order_id_, order_line_id_);}
  
private:
  int order_id_ = 0;
  int order_line_id_ = 0;
};
 
auto main() -> int {
  auto set = hash_set<order_order_line> {
    order_order_line {1, 1},
    order_order_line {1, 1},
    order_order_line {1, 2}
  };
  
  console::write_line("Item count: {}.", set.size());
}
 
// This code produces the following output :
//
// Item count: 2.

Remarks

You can use xtd::hash_code to combine multiple values (for example, fields on a structure or class) into a single hash code. This structure has static and instance methods that operate differently:

* The static methods accept a set of several values to combine.

* Two instance methods operate in a streaming fashion, accepting values one at a time.

Warning

It's best-practice to consider hash codes as an implementation detail, as the implementation may change across xtd versions. Do not store hash codes produced by xtd::hash_code in serialized structures, for example, on-disk. xtd::hash_code uses a statically initialized random seed to enforce this best practice, meaning that the hash codes are only deterministic within the scope of an operating system process.

Examples

generic_icollection.cpp, and generic_ilist.cpp.

Public Constructors
	hash_code ()=default
	Create a new instance of the class hash_code.

Public Methods
template<typename type_t >
hash_code &	add (const type_t value) noexcept
	Adds a single value to the hash code.
bool	equals (const xtd::object &other) const noexcept override
	Determines whether the specified object is equal to the current object.
xtd::size	get_hash_code () const noexcept override
	Serves as a hash function for a particular type.
xtd::size	to_hash_code () const noexcept
	Calculates the final hash code after consecutive xtd::hash_code::add invocations.

Public Static Methods
template<typename ... args_t>
static xtd::size	combine (args_t... values) noexcept
	Combines values into a hash code.

Additional Inherited Members
Public Member Functions inherited from xtd::object
	object ()=default
	Create a new instance of the ultimate base class object.
virtual type_object	get_type () const noexcept
	Gets the type of the current instance.
template<typename object_t >
xtd::uptr< object_t >	memberwise_clone () const
	Creates a shallow copy of the current object.
virtual xtd::string	to_string () const noexcept
	Returns a xtd::string that represents the current object.
Static Public Member Functions inherited from xtd::object
template<typename object_a_t , typename object_b_t >
static bool	equals (const object_a_t &object_a, const object_b_t &object_b) noexcept
	Determines whether the specified object instances are considered equal.
template<typename object_a_t , typename object_b_t >
static bool	reference_equals (const object_a_t &object_a, const object_b_t &object_b) noexcept
	Determines whether the specified object instances are the same instance.

Constructor & Destructor Documentation

hash_code()

xtd::hash_code::hash_code ( )

default

Create a new instance of the class hash_code.

Member Function Documentation

add()

template<typename type_t >

hash_code & xtd::hash_code::add ( const type_t  value )

inlinenoexcept

Adds a single value to the hash code.

Template Parameters

type_t

The type of the value to add to the hash code.

Parameters

value

The value to add to the hash code.

Returns

The current instance.

equals()

bool xtd::hash_code::equals ( const xtd::object &  obj ) const

overridevirtualnoexcept

Determines whether the specified object is equal to the current object.

Parameters

obj	The object to compare with the current object.

Returns

true if the specified object is equal to the current object. otherwise, false.

Examples

The following code example compares the current instance with another object.

#include <xtd/console>
 
using namespace xtd;
 
auto main() -> int {
  auto object1 = new_ptr<object>();
  auto object2 = new_ptr<object>();
  
  auto object3 = object2;
  console::write_line(object1->equals(*object3));
  console::write_line(*object1 == *object3);
  object3 = object1;
  console::write_line(object1->equals(*object3));
  console::write_line(*object1 == *object3);
}
 
// This code produces the following output :
//
// false
// false
// true
// true

Reimplemented from xtd::object.

get_hash_code()

xtd::size xtd::hash_code::get_hash_code ( ) const

overridevirtualnoexcept

Serves as a hash function for a particular type.

Returns

size_t A hash code for the current object.

Reimplemented from xtd::object.

to_hash_code()

xtd::size xtd::hash_code::to_hash_code ( ) const

noexcept

Calculates the final hash code after consecutive xtd::hash_code::add invocations.

Returns

The calculated hash code.

Remarks

This method must be called at most once per instance of xtd::hash_code.

combine()

template<typename ... args_t>

static xtd::size xtd::hash_code::combine ( args_t...  values )

inlinestaticnoexcept

Combines values into a hash code.

Parameters

values

The values to combine into the hash code.

Returns

The hash code that represents the values.

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

• xtd.core/include/xtd/hash_code.h