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 678 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 681 of file ct_utils.h.

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

Referenced by Option(), Option(), and transform().

Option() [2/3]

template<typename T>

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

inlineexplicitconstexpr

Construct a set option with the provided value.

Definition at line 684 of file ct_utils.h.

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

References Option().

Option() [3/3]

template<typename T>

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

inlineconstexpr

Construct an unset option with a default inner value.

Definition at line 687 of file ct_utils.h.

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

References Option().

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 738 of file ct_utils.h.

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

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 692 of file ct_utils.h.

{ return m_has_value; }

Referenced by Botan::map_to_curve_sswu().

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 747 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 702 of file ct_utils.h.

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

References Option().

value()

template<typename T>

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

inlineconstexpr

Either returns the value or throws an exception.

Definition at line 707 of file ct_utils.h.

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

References 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 716 of file ct_utils.h.

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

Referenced by Botan::map_to_curve_sswu().

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 727 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