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Diffstat (limited to 'bindings/cpp/include/serd/Optional.hpp')
-rw-r--r-- | bindings/cpp/include/serd/Optional.hpp | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/bindings/cpp/include/serd/Optional.hpp b/bindings/cpp/include/serd/Optional.hpp new file mode 100644 index 00000000..965e5f1a --- /dev/null +++ b/bindings/cpp/include/serd/Optional.hpp @@ -0,0 +1,151 @@ +// Copyright 2019-2021 David Robillard <d@drobilla.net> +// SPDX-License-Identifier: ISC + +#ifndef SERD_OPTIONAL_HPP +#define SERD_OPTIONAL_HPP + +#include <cassert> +#include <type_traits> +#include <utility> + +namespace serd { + +/** + @defgroup serdpp_optional Optional + @ingroup serdpp + @{ +*/ + +struct ConstructNullOptional {}; + +/// Special tag for constructing an unset Optional +struct Nullopt { + enum class Construct { internal }; + + explicit constexpr Nullopt(Construct) {} +}; + +/** + A simple optional wrapper around a wrapped type with a pointer-like API + + This works like a typical optional type, but only works with Wrapper types, + and exploits the fact that these are interally just pointers to avoid adding + space overhead for an "is_set" flag, like a generic optional class would. + + Types must explicitly opt-in to being optional by providing a constructor + that takes a single ContructNullOptional argument. This constructor should + only be used by the Optional implementation, which guarantees that such an + object will not be used except by calling its cobj() method. +*/ +template<class T> +class Optional +{ +public: + /// The type of the underlying C object + using CType = typename T::CType; + + /// Constructs an empty optional + Optional() = default; + + /// Constructs an empty optional + // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions) + Optional(Nullopt) {} + + /// Constructs an optional that contains the given value + // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions) + Optional(T value) + : _value{std::move(value)} + {} + + /// Constructs an optional that contains a converted value + template< + typename U, + typename = typename std::enable_if<std::is_convertible<U, T>::value>::type> + // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions) + Optional(U&& value) + : _value{std::forward<U>(value)} + {} + + /// Destroys any contained value + void reset() { _value = T{nullptr}; } + + /// Accesses the contained value + const T& operator*() const + { + assert(_value.cobj()); + return _value; + } + + /// Accesses the contained value + T& operator*() + { + assert(_value.cobj()); + return _value; + } + + /// Accesses the contained value + const T* operator->() const + { + assert(_value.cobj()); + return &_value; + } + + /// Accesses the contained value + T* operator->() + { + assert(_value.cobj()); + return &_value; + } + + /// Tests if optional objects are equal + bool operator==(const Optional& optional) + { + return (!*this && !optional) || + (*this && optional && _value == optional._value); + } + + /// Tests if optional objects are not equal + bool operator!=(const Optional& optional) { return !operator==(optional); } + + /// Returns true if this optional contains a value + explicit operator bool() const { return _value.cobj(); } + + /// Returns true if this optional does not contain a value + bool operator!() const { return !_value.cobj(); } + + /// Return a pointer to the underlying C object, or null + CType* cobj() { return _value.cobj(); } + + /// Return a pointer to the underlying C object, or null + const CType* cobj() const { return _value.cobj(); } + +private: + T _value{nullptr}; +}; + +/// Creates an optional object from `value` +template<class T> +constexpr Optional<std::decay_t<T>> +make_optional(T&& value) +{ + return Optional<T>{std::forward<T>(value)}; +} + +/// Creates an optional object with a value constructed in-place from `args` +template<class T, class... Args> +constexpr Optional<T> +make_optional(Args&&... args) +{ + return Optional<T>{std::forward<Args>(args)...}; +} + +/// Constant that represents an empty optional +static constexpr Nullopt nullopt{Nullopt::Construct::internal}; + +/** + @} +*/ + +} // namespace serd + +#endif // SERD_OPTIONAL_HPP |