docs/clang-tidy/checks/performance-unnecessary-copy-initialization.rst

.. title:: clang-tidy - performance-unnecessary-copy-initialization

performance-unnecessary-copy-initialization
===========================================

Finds local variable declarations that are initialized using the copy
constructor of a non-trivially-copyable type but it would suffice to obtain a
const reference.

The check is only applied if it is safe to replace the copy by a const
reference. This is the case when the variable is const qualified or when it is
only used as a const, i.e. only const methods or operators are invoked on it, or
it is used as const reference or value argument in constructors or function
calls.

Example:

.. code-block:: c++

  const string& constReference();
  void Function() {
    // The warning will suggest making this a const reference.
    const string UnnecessaryCopy = constReference();
  }

  struct Foo {
    const string& name() const;
  };
  void Function(const Foo& foo) {
    // The warning will suggest making this a const reference.
    string UnnecessaryCopy1 = foo.name();
    UnnecessaryCopy1.find("bar");

    // The warning will suggest making this a const reference.
    string UnnecessaryCopy2 = UnnecessaryCopy1;
    UnnecessaryCopy2.find("bar");
  }

Options
-------

.. option:: AllowedTypes

   A semicolon-separated list of names of types allowed to be initialized by
   copying. Regular expressions are accepted, e.g. `[Rr]ef(erence)?$` matches
   every type with suffix `Ref`, `ref`, `Reference` and `reference`. The
   default is empty.