clang-tidy - modernize-use-nodiscard — Extra Clang Tools 13 documentation

# Extra Clang Tools 13 documentation

## clang-tidy - modernize-use-nodiscard

# modernize-use-nodiscard

Adds `[[nodiscard]]` attributes (introduced in C++17) to member functions in order to highlight at compile time which return values should not be ignored.

Member functions need to satisfy the following conditions to be considered by this check:

> - no `[[nodiscard]]`, `[[noreturn]]`, `__attribute__((warn_unused_result))`, `[[clang::warn_unused_result]]` nor `[[gcc::warn_unused_result]]` attribute,

> - non-void return type,

> - non-template return types,

> - const member function,

> - non-variadic functions,

> - no non-const reference parameters,

> - no pointer parameters,

> - no template parameters,

> - no template function parameters,

> - not be a member of a class with mutable member variables,

> - no Lambdas,

> - no conversion functions.

Such functions have no means of altering any state or passing values other than via the return type. Unless the member functions are altering state via some external call (e.g. I/O).

## Example

    bool empty() const;
    bool empty(int i) const;

transforms to:

    [[nodiscard]] bool empty() const;
    [[nodiscard]] bool empty(int i) const;

## Options

ReplacementString

  Specifies a macro to use instead of `[[nodiscard]]`. This is useful when maintaining source code that needs to compile with a pre-C++17 compiler.

### Example

    bool empty() const;
    bool empty(int i) const;

transforms to:

    NO_DISCARD bool empty() const;
    NO_DISCARD bool empty(int i) const;

if the `ReplacementString` option is set to NO_DISCARD.

Note

If the `ReplacementString` is not a C++ attribute, but instead a macro, then that macro must be defined in scope or the fix-it will not be applied.

Note

For alternative `__attribute__` syntax options to mark functions as `[[nodiscard]]` in non-c++17 source code. See https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result