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Discard - A _ acts as a placeholder for a variable

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The _ character serves as a discard, which is a placeholder for an unused variable.

There are two uses for the discard token:

  1. To declare an unused variable. A discard can't be read or accessed.
    • Unused out arguments: var r = M(out int _, out var _, out _);
    • Unused lambda expression parameters: Action<int> _ => WriteMessage();
    • Unused deconstruction arguments: (int _, var answer) = M();
  2. To match any expression in a discard pattern. You can add a _ pattern to satisfy exhaustiveness requirements.

The _ token is a valid identifier in C#. The _ token is interpreted as a discard only when no valid identifier named _ is found in scope.

A discard can't be read as a variable. The compiler reports an error if your code reads a discard. The compiler can avoid allocating the storage for a discard in some situations where that is safe.

See also