Using GeneratedRegex (Source Generator)

Use GeneratedRegexAttribute for compile-time regex generation instead of runtime new Regex() .

Why GeneratedRegex?

Aspect Runtime Regex GeneratedRegex

Compilation Runtime Compile-time

Performance Slower first match Pre-compiled, faster

AOT Support Limited Full support

Memory Allocates at runtime No runtime allocation

.NET Version All .NET 7+

Basic Pattern

public partial class EmailValidator { [GeneratedRegex(@"^[\w.-]+@[\w.-]+.\w+$", RegexOptions.IgnoreCase)] private static partial Regex EmailPattern();

public bool IsValidEmail(string email)
{
    return EmailPattern().IsMatch(email);
}

}

Requirements:

• Class must be partial

• Method must be static partial returning Regex

• .NET 7 or later

Common Patterns

Email Validation

public partial class ValidationPatterns { [GeneratedRegex(@"^[\w.-]+@[\w.-]+.\w+$", RegexOptions.IgnoreCase)] public static partial Regex Email(); }

Phone Number

[GeneratedRegex(@"^\d{3}-\d{3,4}-\d{4}$")] public static partial Regex PhoneNumber();

URL Pattern

[GeneratedRegex(@"^https?://[\w.-]+(?:/[\w.-])$", RegexOptions.IgnoreCase)] public static partial Regex Url();

Whitespace Normalization

[GeneratedRegex(@"\s+")] private static partial Regex WhitespacePattern();

public string NormalizeWhitespace(string input) { return WhitespacePattern().Replace(input, " "); }

Migration from Runtime Regex

Before (Runtime)

// Anti-pattern: Runtime compilation public class Validator { private static readonly Regex _emailRegex = new(@"^[\w.-]+@[\w.-]+.\w+$", RegexOptions.Compiled);

public bool IsValid(string email)
{
    return _emailRegex.IsMatch(email);
}

}

After (Source Generator)

// Best practice: Compile-time generation public partial class Validator { [GeneratedRegex(@"^[\w.-]+@[\w.-]+.\w+$")] private static partial Regex EmailPattern();

public bool IsValid(string email)
{
    return EmailPattern().IsMatch(email);
}

}

RegexOptions

// Multiple options [GeneratedRegex(@"pattern", RegexOptions.IgnoreCase | RegexOptions.Multiline)] private static partial Regex MultiOptionPattern();

// With timeout (for untrusted input) [GeneratedRegex(@"complex.*pattern", RegexOptions.None, matchTimeoutMilliseconds: 1000)] private static partial Regex SafePattern();

WPF Validation Example

public partial class FormViewModel : ObservableValidator { [GeneratedRegex(@"^[\w.-]+@[\w.-]+.\w+$", RegexOptions.IgnoreCase)] private static partial Regex EmailPattern();

[GeneratedRegex(@"^\d{3}-\d{3,4}-\d{4}$")]
private static partial Regex PhonePattern();

[CustomValidation(typeof(FormViewModel), nameof(ValidateEmail))]
[ObservableProperty] private string _email = string.Empty;

[CustomValidation(typeof(FormViewModel), nameof(ValidatePhone))]
[ObservableProperty] private string _phone = string.Empty;

public static ValidationResult? ValidateEmail(string email, ValidationContext context)
{
    if (string.IsNullOrEmpty(email))
        return new ValidationResult("Email is required");

    if (!EmailPattern().IsMatch(email))
        return new ValidationResult("Invalid email format");

    return ValidationResult.Success;
}

public static ValidationResult? ValidatePhone(string phone, ValidationContext context)
{
    if (string.IsNullOrEmpty(phone))
        return ValidationResult.Success; // Optional field

    if (!PhonePattern().IsMatch(phone))
        return new ValidationResult("Format: 000-0000-0000");

    return ValidationResult.Success;
}

}

GlobalUsings.cs

global using System.Text.RegularExpressions;

Checklist

• Class is marked as partial

• Method is static partial returning Regex

• Pattern string is valid regex

• Target framework is .NET 7+

• Consider RegexOptions for case sensitivity

• Add timeout for untrusted input patterns