20 General utilities library [utilities]

20.18 Execution policies [execpol]

20.18.3 Execution policy type trait [execpol.type]

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template<class T> struct is_execution_policy { see below };
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is_­execution_­policy can be used to detect execution policies for the purpose of excluding function signatures from otherwise ambiguous overload resolution participation.
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is_­execution_­policy<T> is a Cpp17UnaryTypeTrait with a base characteristic of true_­type if T is the type of a standard or implementation-defined execution policy, otherwise false_­type.
[Note 1:
This provision reserves the privilege of creating non-standard execution policies to the library implementation.
— end note]
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The behavior of a program that adds specializations for is_­execution_­policy is undefined.