.. SPDX-FileCopyrightText: 2024 The IceTray Contributors
..
.. SPDX-License-Identifier: BSD-2-Clause

Avoid Providing Implicit Conversions
------------------------------------

Constructors that can be called with one argument and are not declared
``explicit`` interact poorly with overloading and foster invisible temporary
objects that pop up all over.  Conversions defined as member functions of the
form ``operator T`` (where "T" is a type) are no better -- they interact poorly
with implicit constructors and can allow all sorts of nonsensical code to
compile.

.. highlight:: c++

Example::

    struct Bar
    {
        Bar();      // default constructor
        Bar( int ); // value constructor with implicit conversion
    };

    void func( const Bar& );

    Bar b;
    b = 1; // expands to b.operator=( Bar( 1 ));
    func( 10 ); // expands to func( Bar( 10 ));


``b = 1;`` is allowed and is bad because simple syntax hides potentially
expensive operations - construction of temporary, copy, destruction of
temporary.  To avoid this use explicit: ``explicit Bar( int );``