Type trait
A type trait is a compile-time facility that queries or transforms a type and produces a result representing the requested property or type.
Modern C, Third Edition
A type trait is a compile-time operation that queries a property of a type and produces a result representing that property.
- How it is used
- Enables efficient type-generic features by querying argument-type properties at compile time.
- How deep it goes
- Develops macro requirements and implementation strategies for constants, integer types, VLAs, and pointer qualifiers.
- Examples
- Uses tozero, tonull, isinteger, isvla, pointer-qualification tests, and a type-directed pow macro.
- What you can do after
- Build compile-time type-trait macros that return boolean integer constant expressions without evaluating their arguments.
Learn C++ by Example
A type trait is a compile-time facility that exposes a property or transformation of a C++ type.
- How it is used
- Uses type traits to interrogate types and check whether template-related requirements are satisfied.
- How deep it goes
- Defines traits through a clock-checking example and stops short of detailing trait implementation internals.
- Examples
- Demonstrates std::chrono::is_clock<int>::value as a false result for a non-clock type.
- What you can do after
- Evaluate whether a type satisfies named requirements by reading a trait's Boolean value.
Related concepts
- is_constructibleincludes · is_constructible is a C++ type trait that determines whether a type can be constructed from a specified set of argument types.
- typeof operatorused by · A typeof operator obtains type information about an operand or expression, yielding a type or a string describing its type depending on the language.
- _Genericused by · _Generic is a C11 primary expression that selects one expression from type-associated alternatives according to the type of a controlling expression.
- type_traits headerused by · The type_traits header is the C++ standard library header that declares compile-time type property queries and transformations.
- special member functionmeasures · A special member function is a C++ member function with compiler-recognized semantics for object initialization, copying, moving, or destruction.
- traitcontrasts with · A trait is a type-level construct that defines reusable behavior or members that types can implement or compose.
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