Background and motivation

The .NET regex engine today works based on an NFA/backtracking-based engine. For .NET 7, we're exploring adding an opt-in DFA-based engine. To opt-in, we'd use a new RegexOptions enum value.

API Proposal

namespace System.Text.RegularExpressions
{
     public enum RegexOptions
     {
          ...
          Constrained = 0x0400
     }
}

Other name choices could include DFA, Deterministic, Safe, Predictable, ...

API Usage

var r = new Regex(..., RegexOptions.Constrained);

Risks

It is opt-in as the engine will almost certainly have some limitations on what patterns are supported (e.g. look behinds), impact on capture semantics, etc.