Discard - A _ acts as a placeholder for a variable

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

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The documentation identifies any feature first introduced in the last three versions of the language or in current public previews.

Use the discard token in two ways:

1. To declare an unused variable. You can't read or access a discard.
   • 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 compiler interprets the _ token as a discard only when it doesn't find a valid identifier named _ in scope.

You can't read a discard as a variable. If your code reads a discard, the compiler reports an error. In some situations, the compiler can avoid allocating storage for a discard when it's safe to do so.

See also

• Tuples
• Deconstruction
• Discard pattern