Botan::CT::Option< T > Class Template Reference

#include <ct_utils.h>

Public Member Functions
constexpr std::optional< T >	as_optional_vartime () const
constexpr Choice	has_value () const
	Return true if this Option contains a value.
constexpr CT::Option< T >	operator&& (CT::Choice also)
	Return a new CT::Option that is set if also is set as well.
constexpr	Option ()
	Construct an unset option with a default inner value.
constexpr	Option (T v)
	Construct a set option with the provided value.
constexpr	Option (T v, Choice valid)
	Construct an Option which contains the specified value, and is set or not.
template<std::invocable< const T & > F>
constexpr auto	transform (F f) const -> Option< std::remove_cvref_t< std::invoke_result_t< F, const T & > > >
constexpr const T &	value () const
	Either returns the value or throws an exception.
constexpr T	value_or (T other) const
constexpr T	value_or (T other) const

Detailed Description

template<typename T>
class Botan::CT::Option< T >

A CT::Option<T> is either a valid T, or not

To maintain constant time behavior a value must always be stored. A CT::Choice tracks if the value is valid or not. It is not possible to access the inner value if the Choice is unset.

Definition at line 622 of file ct_utils.h.

Constructor & Destructor Documentation

Option() [1/3]

template<typename T >

Botan::CT::Option< T >::Option ( T v, Choice valid )

inlineconstexpr

Construct an Option which contains the specified value, and is set or not.

Definition at line 625 of file ct_utils.h.

: m_has_value(valid), m_value(std::move(v)) {}

Option() [2/3]

template<typename T >

Botan::CT::Option< T >::Option ( T v )

inlineconstexpr

Construct a set option with the provided value.

Definition at line 628 of file ct_utils.h.

: Option(std::move(v), Choice::yes()) {}

Option() [3/3]

template<typename T >

Botan::CT::Option< T >::Option ( )

inlineconstexpr

Construct an unset option with a default inner value.

Definition at line 631 of file ct_utils.h.

            : Option(T(), Choice::no()) {}

Member Function Documentation

as_optional_vartime()

template<typename T >

std::optional< T > Botan::CT::Option< T >::as_optional_vartime ( ) const

inlineconstexpr

Convert this Option into a std::optional

This is not constant time, leaking if the Option had a value or not

Definition at line 682 of file ct_utils.h.

                                                           {
         if(m_has_value.as_bool()) {
            return {m_value};
         } else {
            return {};
         }
      }

References Botan::CT::Choice::as_bool().

has_value()

template<typename T >

Choice Botan::CT::Option< T >::has_value ( ) const

inlineconstexpr

Return true if this Option contains a value.

Definition at line 636 of file ct_utils.h.

{ return m_has_value; }

operator&&()

template<typename T >

CT::Option< T > Botan::CT::Option< T >::operator&& ( CT::Choice also )

inlineconstexpr

Return a new CT::Option that is set if also is set as well.

Definition at line 691 of file ct_utils.h.

{ return CT::Option<T>(m_value, m_has_value && also); }

transform()

template<typename T >

template<std::invocable< const T & > F>

auto Botan::CT::Option< T >::transform ( F f ) const -> Option<std::remove_cvref_t<std::invoke_result_t<F, const T&>>>

inlineconstexpr

Apply a function to the inner value and return a new Option which contains that value. This is constant time only if f is.

Note

The function will always be called, even if the Option is None. It must be prepared to handle any possible state of T.

Definition at line 646 of file ct_utils.h.

                                                                                                        {
         return {f(m_value), m_has_value};
      }

value()

template<typename T >

const T & Botan::CT::Option< T >::value ( ) const

inlineconstexpr

Either returns the value or throws an exception.

Definition at line 651 of file ct_utils.h.

                                       {
         BOTAN_STATE_CHECK(m_has_value.as_bool());
         return m_value;
      }

References Botan::CT::Choice::as_bool(), and BOTAN_STATE_CHECK.

value_or() [1/2]

template<typename T >

T Botan::CT::Option< T >::value_or ( T other ) const

inlineconstexpr

Returns either the inner value or the alternative, in constant time

This variant is used for types which explicitly define a function conditional_assign which takes a CT::Choice as the conditional.

Definition at line 660 of file ct_utils.h.

      {
         other.conditional_assign(m_has_value, m_value);
         return other;
      }

value_or() [2/2]

template<typename T >

T Botan::CT::Option< T >::value_or ( T other ) const

inlineconstexpr

Returns either the inner value or the alternative, in constant time

This variant is used for integer types where CT::Mask can perform a constant time selection

Definition at line 671 of file ct_utils.h.

      {
         auto mask = CT::Mask<T>::from_choice(m_has_value);
         return mask.select(m_value, other);
      }

References Botan::CT::Mask< T >::from_choice().

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

• src/lib/utils/ct_utils.h