4a88884b39
* Add ranges * Initial Hugo setup * Work in progress * Added selection for local or remote site * Updated to 'light' theme * Changed to using Hextra Hugo theme * Changed to using Hextra Hugo theme * Changed to Hextra Hugo theme * Change to Hextra Hugo theme * Updated Hugo setup. * Updated Hugo setup. # Conflicts: # docs/releases/_index.md * Work in progress * Added new fonts Added new documentation * Latest documentation updates * Latest documentation updates # Conflicts: # docs/containers/array.md # docs/containers/array_view.md # docs/containers/array_wrapper.md # docs/containers/bip_buffer_spsc_atomic.md # docs/containers/bitset.md # docs/containers/indirect_vector.md # docs/containers/vector.md # docs/getting-started/compilers.md * Added bloom_filter markdown doc * Added more documentation Updated CSS for light and dark modes * Fixed some menus Added mode documentation files * Updated CSS rules Added badges to home page Added uniqur_ptr + pool tutorial * Fixed formatting on the home page markdown Modified light amd dark code formatting * Updated unique_ptr-with-pool * Added container and shared message tutorials * Updates to documentation * Added const_multimap * Updated source-formatting.md * Added initial raw text files form Web site editor * Innore coverage build directory * Exported raw text documentation files from the web site editor * Hugo updates * Added Hugo intalation and markdown descriptions * More addition to the documentation * Added closure.md and updates to delegate.md * Added format.md * Added documentation for etl::delegate_observable, etl::function, Base64 codec * Added io_port documentation * Added basic_format_spec * Added documentation for string_stream and string utilities. * Added more documentation Updated the documentation CSS * Added documentation for clocks, day, duration * Added more documentation for chrono classes Updated callouts * More chrono documentation * Completed chrono documentation * Maths functions documentation * Completed maths documentation * Completed maths documentation * Completed maths documentation * Completed maths documentation * Added multiple documentation files * Added iterator.md * Added debug_count.md and versions.md * Added debug_count.md and versions.md * Added more documentation * More documentation * Added some design pattern documentation Modified some of the layout files Modified the About documentation * Converted more documentation pages Modified the site CSS * Added more documentation Moced some documentation files to new directories * Added more documentation Tweaks to CSS * Added callback_timer_deferred_locked documentation * Added callback_timer_locked documentation * More documentation updates * More documentation updates * More documentation updates * New documentation files. Harmonised file name format * New documentation files. * Multiple document updates * Multiple document updates * Final conversion of web pages * Updates before PR * Updates before PR * Updates before PR # Conflicts: # docs/blog/_index.md * Final pre PR updates * Updates to message framework documentation * Renamed directory * Fix spelling * Added author and date to blog files Moved documentation files merged from development * Fixed 'Description' typo * Fix typos # Conflicts: # docs/IO/io_port.md # docs/containers/sets/const-multiset.md # docs/containers/sets/const-set.md # docs/maths/correlation.md # docs/maths/gamma.md * Renamed two files to lower case * Minor renaming * Added author and date * Updated callout on bresenham_line.md Added support for showing the ETL version on the documentation first page, by copying the version.txt file as a hugo asset. Updated the Python 'update_release.py' to copy 'version.txt' * Replace space in filename with hyphen. Added more information to hugo-commands.md * Replace space in filename with hyphen. Added more information to hugo-commands.md # Conflicts: # docs/getting-started/view-the-docs-locally/hugo-commands.md * Added a link to pseudo_moving_average.md * Updated title pages for groups * Fixed missing 404 for non-existent pages * Fixed coordinate variable names in the 'Calculating the intersection' example --------- Co-authored-by: Roland Reichwein <Roland.Reichwein@bmw.de> Co-authored-by: John Wellbelove <john.wellbelove@etlcpp.com> Co-authored-by: John Wellbelove <john.wellbelove@etlcpp.co.uk>
4.5 KiB
| title |
|---|
| optional |
{{< callout type="info">}}
Header: optional.h
Similar to: std::optional
{{< /callout >}}
A class where the value is optional.
If a value is not assigned then an object of the contained type is not constructed.
template <typename T>
etl::optional<T>
If _DEBUG is defined then accesses to invalid data is detected either by throwing (ETL_THROW_EXCEPTIONS defined) or calling the error handler.
Template deduction guides
C++17 and above
template <typename T>
etl::optional(T)
-> etl::optional<T>
Example
std::string text = "Hello";
etl::optional opt{ text };
Defines opt as containing a std::string, containing the supplied text.
Constructor
optional()
Description
Default constructor.
optional(const T& value)
optional(T&& value)
Description
Construct from value. Constructs a T.
optional(const optional<T>& other)
optional(optional<T>&& other)
Description
Construct copy. Constructs a T.
optional(nullopt)
Description
Construct empty value (same as default constructor).
template <typename... TArgs>
ETL_CONSTEXPR14
optional_impl(etl::in_place_t, TArgs&&... args)
Description
Constructor from variadic args.
20.43.0
template <typename U, typename... TArgs>
ETL_CONSTEXPR14
optional_impl(etl::in_place_t, std::initializer_list<U> ilist, TArgs&&... args)
Description
Constructor from variadic args.
20.43.0
~optional()
Description
Destructor.
Destructs a T if a value has been assigned.
Operations
optional& operator =(etl::nullopt)
Description
Clears the optional.
optional& operator =(const optional<T>& value)
optional& operator =(optional<T>&& value)
Description
Copy constructor.
optional& operator =(const T& value)
optional& operator =(T&& value)
Description
Assigns a value to the optional.
Note
Unlike std::optional, assigning from { } will not clear the optional item to 'empty'.
It will be assigned a default constructed 'T'.
etl::optional<int> opt;
opt = { }; // opt will contain 0.
void swap(optional& other)
Description
Swaps with the other optional
void reset()
Description
Resets the optional back to default.
emplace
Description
Construct in-place from arguments.
C++03
template <typename T1>
void emplace(const T1& value1)
template <typename T1, typename T2>
void emplace(const T1& value1, const T2& value2)
template <typename T1, typename T2, typename T3>
void emplace(const T1& value1, const T2& value2, const T3& value3)
template <typename T1, typename T2, typename T3, typename T4>
void emplace(const T1& value1, const T2& value2, const T3& value3, const T4& value4)
C++11
template <typename ... Args>
void emplace(Args && ... args)
Observers
const T& value() const
T& value()
Description
Returns the contained value.
template <typename T>
T value_or(T value)
Description
Returns the contained value if *this is valid, otherwise returns value.
const T* operator->() const
T* operator->()
Description
Returns a pointer to the contained value.
const T& operator *() const
T* operator *()
Description
Returns a reference to the contained value.
Tests
explicit operator bool() const
bool has_value() const
Description
Checks whether *this is in a valid state, i.e. whether the contained value is initialised.
Returns true if valid, otherwise false.
Non-member functions
operator ==
Description
true if the contents of the lists are equal, otherwise false.
operator !=
Description
true if the contents of the lists are not equal, otherwise false.
operator <
Description
true if the contents of the lhs are lexicographically less than the contents of the rhs, otherwise false.
operator <=
Description
true if the contents of the lhs are lexicographically less than or equal to the contents of the rhs, otherwise false.
operator >
Description
true if the contents of the lhs are lexicographically greater than the contents of the rhs, otherwise false.
operator >=
Description
true if the contents of the lhs are lexicographically greater than or equal to the contents of the rhs, otherwise false.