regex_ex.cs

static class RegexUtil
{
    static readonly memo = new Dictionary<string, Regex>();

    public static bool IsMatch(this string s, RegexOptions? options = null)
    {
        if(!memo.TryGetValue(s, out RegEx rgx))
            memo.Add(s, rgx = new RegEx(s, options ?? RegExOptions.None));
            
        return rgx.IsMatch(s);
    }            
}

//OR

struct regexp
{
    readonly Regex regex;
    
    public regexp(string s) => regex = new Regex(s);
    
    public Match Match(string s) => regex.Match(s);
    public bool IsMatch(string s) => regex.IsMatch(s);
    
    public static implicit operator regexp(string s) => new regexp(s);
}