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var pattern

Context: The var pattern matches any expression and assigns it to a new variable. It is useful in switch expressions to capture the input.

object obj = "test";
if (obj is var x)
{
    Console.WriteLine(x.GetType()); // always matches
}

In switch expressions

string result = obj switch
{
    int i => $"int: {i}",
    string s => $"string: {s}",
    var other => $"unknown: {other.GetType()}"
};

Real-world usage example

Logging the original value: In a switch expression, use var as the default case to capture the unmatched value for logging.

Example: In a logging middleware, you can log the actual value that didn’t match any pattern.