# deduction guides for `std::reference_wrapper`

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< cpp‎ | utility‎ | functional‎ | reference wrapper

Defined in header `<functional>` |  |
template<typename T> reference_wrapper(T&) -> reference_wrapper<T>; |  | (since C++17)

One deduction guide is provided for std::reference_wrapper to support deduction of the sole class template parameter.

### Example

| This section is incomplete Reason: no example

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2981 | C++17 | a redundant deduction guide from `reference_wrapper<T>` was provided | removed
LWG 2993 | C++17 | defect resolution removed a constructor used for class template argument deduction | added deduction guide to compensate

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