# Extra Clang Tools 21.1.6 documentation

## clang-tidy - performance-for-range-copy

# performance-for-range-copy

Finds C++11 for ranges where the loop variable is copied in each iteration but it would suffice to obtain it by const reference.

The check is only applied to loop variables of types that are expensive to copy which means they are not trivially copyable or have a non-trivial copy constructor or destructor.

To ensure that it is safe to replace the copy with a const reference the following heuristic is employed:

1. The loop variable is const qualified.

2. The loop variable is not const, but only const methods or operators are invoked on it, or it is used as const reference or value argument in constructors or function calls.

## Options

WarnOnAllAutoCopies

  When true, warns on any use of `auto` as the type of the range-based for loop variable. Default is false.

AllowedTypes

  A semicolon-separated list of names of types allowed to be copied in each iteration. Regular expressions are accepted, e.g. `[Rr]ef(erence)?$` matches every type with suffix `Ref`, `ref`, `Reference` and `reference`. The default is empty. If a name in the list contains the sequence ::, it is matched against the qualified type name (i.e. `namespace::Type`), otherwise it is matched against only the type name (i.e. `Type`).