clang-tidy - performance-unnecessary-value-param — Extra Clang Tools 13 documentation

# Extra Clang Tools 13 documentation

## clang-tidy - performance-unnecessary-value-param

# performance-unnecessary-value-param

Flags value parameter declarations of expensive to copy types that are copied for each invocation but it would suffice to pass them by const reference.

The check is only applied to parameters of types that are expensive to copy which means they are not trivially copyable or have a non-trivial copy constructor or destructor.

To ensure that it is safe to replace the value parameter with a const reference the following heuristic is employed:

1. the parameter is const qualified;

2. the parameter is not const, but 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:

    void f(const string Value) {
      // The warning will suggest making Value a reference.
    }

    void g(ExpensiveToCopy Value) {
      // The warning will suggest making Value a const reference.
      Value.ConstMethd();
      ExpensiveToCopy Copy(Value);
    }

If the parameter is not const, only copied or assigned once and has a non-trivial move-constructor or move-assignment operator respectively the check will suggest to move it.

Example:

    void setValue(string Value) {
      Field = Value;
    }

Will become:

    #include <utility>

    void setValue(string Value) {
      Field = std::move(Value);
    }

## Options

IncludeStyle

  A string specifying which include-style is used, llvm or google. Default is llvm.

AllowedTypes

  A semicolon-separated list of names of types allowed to be passed by value. Regular expressions are accepted, e.g. [Rr]ef(erence)?$ matches every type with suffix Ref, ref, Reference and reference. The default is empty. If a name in the list contains the sequence :: it is matched against the qualified typename (i.e. namespace::Type, otherwise it is matched against only the type name (i.e. Type).