using-generated-regex

Using GeneratedRegex (Source Generator)

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

Why GeneratedRegex?

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);
    }
}