How deeply does Learn C++ by Example cover type trait?

Defines traits through a clock-checking example and stops short of detailing trait implementation internals.

Type trait

A type trait is a compile-time facility that exposes a property or transformation of a C++ type.

A type trait is a compile-time facility that exposes a property or transformation of a C++ type. Traits let generic code interrogate types before execution. section 6.0 section 4.2.4

The chrono library provides std::chrono::is_clock. Its Boolean value reports whether a type satisfies the clock requirements, such as defining rep, period, duration, time_point, is_steady, and now(). section 4.2.4

Checking a clock type

std::chrono::is_clock<int>::value is false because int is not a clock. Applying the trait can expose an unsuitable type before another time-related function uses it. section 4.2.4

std::chrono::is_clock<int>::value

Inspect the compact expression that queries whether int satisfies the clock requirements. section 4.2.4

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Modern C, Third EditionA type trait is a compile-time operation that queries a property of a type and produces a result representing that property.

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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.

This explainer was generated by Manning's knowledge graph from the text of Learn C++ by Example. The section links point to the parts of the book it draws on.