All Callable Concepts and Invocability Traits

All Callable Concepts and Invocability Traits

A compact scan page for callable-related concepts, invocability traits, and result-type query utilities.

How to use this reference page

Use reference pages to confirm names, categories, nearby facilities, and the constraints that matter before writing or reviewing code.

Scan the top of the page first to identify the primary types, functions, or algorithm families involved.
Use the nearby-page links when your question is really about a companion header, related algorithm family, or broader subsystem.
Validate tricky behavior with a small compileable example before relying on memory for details like invalidation, ordering, allocation, or lifetime rules.

All Callable Concepts and Invocability Traits

Callable concepts

std::invocable
std::regular_invocable
std::predicate
std::relation
std::equivalence_relation
std::strict_weak_order

Invocability traits

std::is_invocable
std::is_invocable_r
std::is_nothrow_invocable
std::is_nothrow_invocable_r
std::invoke_result

std::invoke
std::invoke_r
std::function
std::reference_wrapper

Practical rules

Use concepts in public templates when readability matters.
Use traits inside low-level metaprogramming and compatibility layers.
Prefer expressing callable requirements directly instead of relying on template substitution failures alone.

Example in practice

int main() {
    // Pick one facility from this reference page.
    // Write the smallest program that exercises its main precondition,
    // complexity rule, or lifetime constraint before scaling up.
    return 0;
}