# std::indirect_strict_weak_order

From cppreference.com
< cpp‎ | iterator

Defined in header `<iterator>` |  |

template< class F, class I1, class I2 = I1 >

concept indirect_strict_weak_order =
std::indirectly_readable <I1> &&
std::indirectly_readable <I2> &&
std::copy_constructible <F> &&
std::strict_weak_order
<F&, /*indirect-value-t*/<I1>, /*indirect-value-t*/<I2>> &&
std::strict_weak_order
<F&, /*indirect-value-t*/<I1>, std::iter_reference_t <I2>> &&
std::strict_weak_order
<F&, std::iter_reference_t <I1>, /*indirect-value-t*/<I2>> &&
std::strict_weak_order

<F&, std::iter_reference_t <I1>, std::iter_reference_t <I2>>;

(since C++20)

The concept `indirect_strict_weak_order` specifies requirements for algorithms that call strict weak orders as their arguments. The key difference between this concept and std::strict_weak_order is that it is applied to the types that `I1` and `I2` references, rather than `I1` and `I2` themselves.

### Defect reports

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

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
P2609R3 | C++20 | some requirements were defined in terms of std::iter_value_t <I>& which mishandled projections resulting in incompatibility with strict weak order F& | defined in terms of /*indirect-value-t*/<I> to correctly handle such projections
P2997R1 | C++20 | `indirect_strict_weak_order` required F& to satisfy `strict_weak_order` with std::iter_common_reference_t <I> | does not require

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