c++20-features.md

C++20 Features: https://en.cppreference.com/w/cpp/compiler_support

Language Features

• Allow lambda-capture [=, this]
• __VA_OPT__
• Designated initializers
• template-parameter-list for generic lambdas
• Default member initializers for bit-fields
• Initializer list constructors in class template argument deduction
• const&-qualified pointers to members
• Concepts
• Lambdas in unevaluated contexts
• Three-way comparison operator
• DR: Simplifying implicit lambda capture
• init-statements for range-based for
• Default constructible and assignable stateless lambdas
• const mismatch with defaulted copy constructor
• Access checking on specializations
• ADL and function templates that are not visible
• Less eager instantiation of constexpr functions
• Attributes [[likely]] and [[unlikely]]
• Make typename more optional
• Pack expansion in lambda init-capture
• Attribute [[no_unique_address]]
• DR: Relaxing the structured bindings customization point finding rules
• DR: Relaxing the range-for loop customization point finding rules
• DR: Allow structured bindings to accessible members
• Destroying operator delete
• Class types in non-type template parameters
• Deprecate implicit capture of this via [=]
• explicit(bool)
• Integrating feature-test macros
• Prohibit aggregates with user-declared constructors
• constexpr virtual function
• Consistency improvements for comparisons
• char8_t
• std::is_constant_evaluated()
• constexpr try-catch blocks
• Immediate functions
• Nested inline namespaces
• Yet another approach for constrained declarations
• Signed integers are two's complement
• constexpr dynamic_cast and polymorphic typeid
• Changing the active member of a union inside constexpr
• Coroutines
• Parenthesized initialization of aggregates
• DR: Array size deduction in new-expressions
• Modules
• Stronger Unicode requirements
• <=> != ==
• DR: Explicitly defaulted functions with different exception specifications
• Lambda capture and storage class specifiers of structured bindings
• Permit conversions to arrays of unknown bound
• constexpr container operations
• Deprecating some uses of volatile
• constinit
• Deprecate comma operator in subscripts
• [[nodiscard]] with message
• Trivial default initialization in constexpr functions
• Unevaluated asm-declaration in constexpr functions
• using enum
• Synthesizing three-way comparison for specified comparison category
• DR: [[nodiscard]] for constructors
• Class template argument deduction for alias templates
• Class template argument deduction for aggregates
• DR: Implicit move for more local objects and rvalue references
• Allow defaulting comparisons by value
• Remove std::weak_equality and std::strong_equality
• Inconsistencies with non-type template parameters
• DR: Converting from T* to bool should be considered narrowing

Library Features

• std::endian
• Extending std::make_shared() to support arrays
• Floating point atomic
• Synchronized buffered ostream
• constexpr for <algorithm> and <utility>
• More constexpr for <complex>
• Make std::memory_order a scoped enumeration
• String prefix and suffix checking
• Library support for operator <=> <compare>
• std::remove_cvref
• [[nodiscard]] in the standard library
• Using std::move in numeric algorithms
• Utility to convert a pointer to a raw pointer
• Atomic std::shared_ptr and std::weak_ptr
• std::span
• Calendar and timezone
• <version>
• Comparing unordered containers
• ConstexprIterator requirements
• std::basic_string::reserve() should not shrink
• std::atomic_ref
• contains() member function of associative containers
• DR: Guaranteed copy elision for piecewise construction
• std::bit_cast()
• Integral power-of-2 operations
• Improving the return value of erase-like algorithms
• std::destroying_delete
• std::is_nothrow_convertible
• Add shift to <algorithm>
• Constexpr for std::swap() and swap related functions
• std::type_identity
• Concepts library
• constexpr comparison operators for std::array
• std::unwrap_ref_decay and std::unwrap_reference
• std::bind_front()
• std::reference_wrapper for incomplete types
• Fixing operator>>(basic_istream&, CharT*)
• Library support for char8_t
• Utility functions to implement uses-allocator construction
• DR: std::variant and std::optional should propagate copy/move triviality
• A sane std::variant converting constructor
• std::function's move constructor should be noexcept
• The One Ranges Proposal
• Heterogeneous lookup for unordered containers
• <chrono> zero(), min(), and max() should be noexcept
• constexpr in std::pointer_traits
• std::assume_aligned()
• Remove comparison operators of std::span
• Make stateful allocator propagation more consistent for operator+(basic_string)
• Consistent container erasure
• std::lerp() and std::midpoint()
• Usability enhancements for std::span
• DR: Make create_directory() Intuitive
• std::ssize() and unsigned extent for std::span
• Traits for (un)bounded arrays
• std::to_array()
• Efficient access to std::basic_stringbuf’s Buffer
• Layout-compatibility and pointer-interconvertibility traits
• Bit operations
• Mathematical constants
• Text formatting
• std::stop_token and std::jthread
• constexpr std::allocator and related utilities
• constexpr std::string
• constexpr std::vector
• Input range adaptors
• constexpr std::invoke() and related utilities
• Atomic waiting and notifying, std::counting_semaphore, std::latch and std::barrier
• std::source_location
• Adding <=> to the standard library
• constexpr default constructor of std::atomic and std::atomic_flag
• constexpr for numeric algorithms
• Safe integral comparisons