.. title:: clang-tidy - cppcoreguidelines-prefer-member-initializer

cppcoreguidelines-prefer-member-initializer
===========================================

Finds member initializations in the constructor body which can be  converted
into member initializers of the constructor instead. This not only improves
the readability of the code but also positively affects its performance.
Class-member assignments inside a control statement or following the first
control statement are ignored.

This check implements `C.49
<https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c49-prefer-initialization-to-assignment-in-constructors>`_
from the C++ Core Guidelines.

Please note, that this check does not enforce rule `C.48
<https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c48-prefer-in-class-initializers-to-member-initializers-in-constructors-for-constant-initializers>`_
from the C++ Core Guidelines. For that purpose
see check :doc:`modernize-use-default-member-init
<../modernize/use-default-member-init>`.

Example 1
---------

.. code-block:: c++

  class C {
    int n;
    int m;
  public:
    C() {
      n = 1; // Literal in default constructor
      if (dice())
        return;
      m = 1;
    }
  };

Here ``n`` can be initialized in the constructor initializer list, unlike
``m``, as ``m``'s initialization follows a control statement (``if``):

.. code-block:: c++

  class C {
    int n;
    int m;
  public:
    C(): n(1) {
      if (dice())
        return;
      m = 1;
    }
  };

Example 2
---------

.. code-block:: c++

  class C {
    int n;
    int m;
  public:
    C(int nn, int mm) {
      n = nn; // Neither default constructor nor literal
      if (dice())
        return;
      m = mm;
    }
  };

Here ``n`` can be initialized in the constructor initializer list, unlike
``m``, as ``m``'s initialization follows a control statement (``if``):

.. code-block:: c++

  C(int nn, int mm) : n(nn) {
    if (dice())
      return;
    m = mm;
  }
