[#FOLLY_FOR_EACH_THIS_OVERLOAD_IN_CLASS_BODY_DELEGATE]
= FOLLY_FOR_EACH_THIS_OVERLOAD_IN_CLASS_BODY_DELEGATE
:mrdocs:

FOLLY_FOR_EACH_THIS_OVERLOAD_IN_CLASS_BODY_DELEGATE

== Synopsis

Declared in `<folly/Utility.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
#define FOLLY_FOR_EACH_THIS_OVERLOAD_IN_CLASS_BODY_DELEGATE(MEMBER, DELEGATE)

----

== Description

Helper macro to add 4 delegated, qualifier‐overloaded methods to a class

Example:

template <typename T> class optional { public: bool has_value() const;

T& value() & { if (!has_value()) { throw std::bad_optional_access(); } return m_value; }

const T& value() const& { if (!has_value()) { throw std::bad_optional_access(); } return m_value; }

T&& value() && { if (!has_value()) { throw std::bad_optional_access(); } return std::move(m_value); }

const T&& value() const&& { if (!has_value()) { throw std::bad_optional_access(); } return std::move(m_value); } };

This is equivalent to

template <typename T> class optional { template <typename Self> decltype(auto) value_impl(Self&& self) { if (!self.has_value()) { throw std::bad_optional_access(); } return std::forward<Self>(self).m_value; } // ...

public: bool has_value() const;

FOLLY_FOR_EACH_THIS_OVERLOAD_IN_CLASS_BODY_DELEGATE(value, value_impl); };

Note: This can be migrated to C++23's deducing this: https://www.open‐std.org/jtc1/sc22/wg21/docs/papers/2021/p0847r7.html

== Parameters

[cols="1,4"]
|===
| Name| Description
| *MEMBER*
| Name of the member function to generate.
| *DELEGATE*
| Name of the static implementation to delegate to.
|===


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