Bits of .NET

ArgumentNullException says ‘parameter is null’. Which parameter?

// Old way - manual parameter name
public void Process(User user)
{
    if (user == null)
        throw new ArgumentNullException(nameof(user));
}

// New way - automatic! (C# 10+)
public void Process(User user)
{
    ArgumentNullException.ThrowIfNull(user);
    // Error message includes actual expression: 'user'
}

// Custom validation
public void ValidatePositive(
    int value,
    [CallerArgumentExpression("value")] string? paramName = null)
{
    if (value <= 0)
        throw new ArgumentException($"{paramName} must be positive");
}

// Usage
ValidatePositive(count);
// Error: 'count must be positive' (not 'value')