What are the key language features, library additions, and deprecated elements introduced in C 17?

C 17 Features

C 17 introduces a wealth of new features to the language, significantly expanding its capabilities and enhancing its usability. These additions encompass various aspects of the language, from template improvements and lambda enhancements to library additions and deprecated elements.

Language Features

Templates and Generic Code:

• Template Argument Deduction for Class Templates: Constructors can now deduce template arguments, similar to functions.
• Template Argument: Represents a value of any non-type template argument type.
• Revising Non-Type Template Arguments: Several fixes and revisions have been made to non-type template arguments.

Lambda:

• Constexpr Lambdas: Lambdas can now be explicitly marked as constexpr if they satisfy certain requirements.
• Capturing this in Lambdas: Lambdas can now capture the this pointer, allowing access to member variables and methods.

Attributes:

• New Attributes: Attributes such as [[fallthrough]], [[nodiscard]], and [[maybe_unused]] have been introduced to enhance code clarity and readability.
• Attributes on Namespaces and Enumerators: Attributes can now be applied to namespaces and enumerators using [[attributes]].

Syntax Cleanup:

• Inline Variables: Variables can now be declared inline, allowing the compiler to inline their definitions.
• Simplified Namespace Declaration: The namespace A::B syntax has been introduced for concise namespace declarations.
• Simplified static_assert: static_assert statements can now be used without a string argument.

Clean Multi-Return and Flow Control:

• Structured Bindings: Structured bindings enable more convenient unpacking of tuples and other data structures in declarations.
• Conditional Statements with Initialization: if (init; condition) and switch (init; condition) provide more flexibility in conditional statements.
• Generalizing Range-Based For Loops: Range-based for loops now support sentinels (end iterators) that differ from the beginning iterators.
• if constexpr: if constexpr allows conditional compilation based on compile-time constants.

Other:

• Hexadecimal Float Point Literals: Floating-point literals can now be expressed in hexadecimal format.
• Dynamic Memory Allocation for Over-Aligned Data: Improved support for dynamic memory allocation of over-aligned data.
• Guaranteed Copy Elision: Certain scenarios where copy elision was not guaranteed now have explicit guarantees.
• Improved Order-of-Evaluation: The order-of-evaluation rules for certain expressions have been revised for clearer behavior.

Library Additions

Data Types:

• std::variant: A polymorphic type that can hold a value of one of multiple alternative types.
• std::optional: Represents an optional value that may or may not contain a value.
• std::any: A type-erased container that can hold a value of arbitrary type.
• std::string_view: A reference to a character sequence, similar to const char*.
• std::byte: A type for representing raw bytes.

Utilities:

• std::invoke: Invokes a callable with given arguments, supporting various types of callables.
• std::apply: Unpacks a tuple and passes its elements as arguments to a callable.
• std::invoke_result and Related Concepts: Concepts and types for determining the validity and result of invoking a callable with given arguments.

File System Library (TS v1):

• Classes and functions for working with file systems, directories, and files.

New Algorithms:

• for_each_n
• reduce
• transform_reduce
• exclusive_scan
• inclusive_scan
• transform_exclusive_scan
• transform_inclusive_scan

Threading:

• std::shared_mutex: A shared mutex that allows multiple readers but only one writer.
• atomic::is_always_lockfree: Indicates whether an atomic type is lock-free in all cases.
• scoped_lock:: Locks multiple mutexes simultaneously, simplifying locking and unlocking.

(Partial) Library Fundamentals Library (TS v1):

• Functionality for performing searches and working with polymorphic allocators.

Container Improvements:

• try_emplace and insert_or_assign: Improved container insertion methods for handling specific scenarios.
• Splicing for Containers: Efficiently moving nodes between containers.

Smart Pointer Changes:

• Fixes and tweaks to std::unique_ptr and other smart pointers.

Additional Improvements:

• Trivially Copyable std::reference_wrapper: Improves performance in certain cases.
• Updated C11 Library: The C 17 standard library is based on C11, providing compatibility with modern systems.
• Deprecated Elements: Various elements from previous versions of the C standard have been deprecated.

Features in C 1z (Expected for C 17)**

To determine which features from the C 1z working draft will be available in C 17 compilers, it is recommended to consult the documentation and release notes of individual compilers. Not all features from C 1z will necessarily be implemented in every C 17 compiler.

Please note that not all changes or features have been mentioned in this summary. For a comprehensive list, please refer to the C 17 standard document or other reputable sources.

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