New Features in C 17

Following the completion of feature development for C 17, several new language features and library additions have been introduced:

Language Features:

• Improved Template Usage:

  • Template argument deduction for class templates
  • Representation of values of any type with template

• Lambda Enhancements:

  • Introduction of constexpr lambdas
  • Ability to capture this in lambdas

• Attributes:

  • Introduction of new attributes, such as [[fallthrough]], [[nodiscard]], and [[maybe_unused]]

• Syntax Cleanup:

  • Inline variables
  • Simplified namespace syntax: namespace A::B
  • No-throw expressions: throw() and noexcept(true)

• Control Flow Improvements:

  • Structured bindings for unpacking values
  • if (init; condition) and switch (init; condition) for enhanced flow control
  • Generalized range-based for loops
  • if constexpr for conditional compilation

• Other Notable Features:

  • Hexadecimal float point literals
  • Dynamic memory allocation for over-aligned data
  • Guaranteed copy elision
  • Fixed order-of-evaluation for expressions
  • Direct list-initialization of enums
  • Forward progress guarantees for threads

Library Additions:

Data Types:

• std::variant for representing values of different types
• std::optional for representing optional values
• std::any for representing values of any type, including non-copyable types
• std::string_view for efficient handling of string references
• std::byte for representing data without type information

Callable Handling:

• std::invoke for generic callable invocation
• std::apply for tuple-based callable invocation
• std::make_from_tuple for constructing objects from tuples
• Introduction of is_invocable and related traits

File System Library:

• Implementation of the File System Technical Specification (TS)

New Algorithms:

• for_each_n, reduce, transform_reduce, and more

Threading Enhancements:

• Introduction of std::shared_mutex for more efficient multi-threaded access
• Atomic guarantees and hardware interference size detection

Library Fundamentals TS Additions:

• Searching algorithms (alg.search)
• Polymorphic allocator (pmr)

Container Improvements:

• try_emplace and insert_or_assign for efficient container insertion
• Splicing for maps, sets, and unordered containers
• Non-const data() access for strings

Smart Pointers:

• Fixes and tweaks to unique_ptr
• Introduction of weak_from_this for managing shared pointers

Misc:

• Use of C11 instead of C99 for the standard library
• Reserved std[0-9] namespaces for future standard libraries
• Various utility functions (destroy, uninitialized_***)
• Exposure of special math functions
• Introduction of std::clamp, std::gcd, and std::lcm
• Exception handling improvements, including std::uncaught_exceptions
• std::as_const, std::bool_constant, and various template utilities
• Improved std::chrono library
• Introduction of Boolean operators (std::conjunction, std::disjunction, std::negation)
• Rules for noexcept usage within std

Deprecated Features:

• Removal of some C libraries, , result_of, and others