redundantOptionalChaining.qdoc

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// Copyright (C) 2025 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
\page qmllint-warnings-and-errors-redundant-optional-chaining.html
\ingroup qmllint-warnings-and-errors
 
\title Redundant Optional Chaining
\brief [redundant-optional-chaining] Some optional chaining lookups could be non-optional
 
\qmllintwarningcategory redundant-optional-chaining
 
\section1 Redundant Optional Chaining
 
\section2 What happened?
Some lookups use optional chaining when it isn't necessary. This can happen when looking up enum
values or when performing a lookup on a base that cannot be \c{null} or \c{undefined}.
 
\section2 Why is this bad?
An optional lookup needs to perform a runtime check that a regular lookup doesn't. These extra
instructions cannot always be determined to be redundant and optimized out by the tooling. They
then add an extra runtime performance cost and bloat the program unnecessarily.
 
Additionally, the warning may hint that the optional lookup was performed on the wrong base in the
chain. See the next section for a more concrete example.
 
\section2 Example
\qml
// Main.qml
import QtQml
 
QtObject {
    // Main will either be resolved and always work, or throw an exception or fail to compile
    enum E { A, B, C }
    property int i: Main?.A
 
    // A url cannot be null or undefined
    property url u: ""
    property string s: u?.toString()
 
    // Did you mean to make the second lookup optional?
    property int i: Safe?.Unsafe.i
}
\endqml
To fix these warnings, replace the redundant optional lookups with non-optional ones:
\qml
// Main.qml
import QtQml
 
QtObject {
    enum E { A, B, C }
    property int i: Main.A
 
    property url u: ""
    property string s: u.toString()
 
    property int i: Safe.Unsafe?.i
}
\endqml
*/