62 lines
2.3 KiB
ReStructuredText
62 lines
2.3 KiB
ReStructuredText
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.. title:: clang-tidy - performance-unnecessary-copy-initialization
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performance-unnecessary-copy-initialization
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===========================================
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Finds local variable declarations that are initialized using the copy
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constructor of a non-trivially-copyable type but it would suffice to obtain a
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const reference.
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The check is only applied if it is safe to replace the copy by a const
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reference. This is the case when the variable is const qualified or when it is
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only used as a const, i.e. only const methods or operators are invoked on it, or
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it is used as const reference or value argument in constructors or function
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calls.
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Example:
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.. code-block:: c++
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const string& constReference();
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void Function() {
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// The warning will suggest making this a const reference.
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const string UnnecessaryCopy = constReference();
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}
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struct Foo {
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const string& name() const;
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};
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void Function(const Foo& foo) {
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// The warning will suggest making this a const reference.
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string UnnecessaryCopy1 = foo.name();
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UnnecessaryCopy1.find("bar");
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// The warning will suggest making this a const reference.
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string UnnecessaryCopy2 = UnnecessaryCopy1;
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UnnecessaryCopy2.find("bar");
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}
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Options
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-------
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.. option:: AllowedTypes
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A semicolon-separated list of names of types allowed to be initialized by
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copying. Regular expressions are accepted, e.g. `[Rr]ef(erence)?$` matches
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every type with suffix `Ref`, `ref`, `Reference` and `reference`. The default
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is empty. If a name in the list contains the sequence `::` it is matched
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against the qualified typename (i.e. `namespace::Type`, otherwise it is
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matched against only the type name (i.e. `Type`).
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.. option:: ExcludedContainerTypes
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A semicolon-separated list of names of types whose methods are allowed to
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return the const reference the variable is copied from. When an expensive to
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copy variable is copy initialized by the return value from a type on this
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list the check does not trigger. This can be used to exclude types known to
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be const incorrect or where the lifetime or immutability of returned
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references is not tied to mutations of the container. An example are view
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types that don't own the underlying data. Like for `AllowedTypes` above,
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regular expressions are accepted and the inclusion of `::` determines whether
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the qualified typename is matched or not.
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