Question

I’m looking at this code, and it is formatting all regular expressions using this function:

string.Format("(?-mix:{0})", regex);

What exactly does (?-mix:{0}) mean? (I know the {0} is a placeholder).

Here is the code:

https://github.com/formosatek/dotliquid/blob/master/src/DotLiquid/Liquid.cs#L36
https://github.com/formosatek/dotliquid/blob/master/src/DotLiquid/Util/R.cs#L12

public static string Q(string regex)
        {
            return string.Format("(?-mix:{0})", regex);
        }


public static class Liquid
    {
        internal static readonly ResourceManager ResourceManager = new ResourceManager(typeof(DotLiquid.Properties.Resources));

        public static readonly string FilterSeparator = R.Q(@"\|");
        public static readonly string ArgumentSeparator = R.Q(@",");
        public static readonly string FilterArgumentSeparator = R.Q(@":");
        public static readonly string VariableAttributeSeparator = R.Q(@".");
        public static readonly string TagStart = R.Q(@"\{\%");
        public static readonly string TagEnd = R.Q(@"\%\}");
        public static readonly string VariableSignature = R.Q(@"\(?[\w\-\.\[\]]\)?");
        public static readonly string VariableSegment = R.Q(@"[\w\-]");
        public static readonly string VariableStart = R.Q(@"\{\{");
        public static readonly string VariableEnd = R.Q(@"\}\}");
        public static readonly string VariableIncompleteEnd = R.Q(@"\}\}?");
        public static readonly string QuotedString = R.Q(@"""[^""]*""|'[^']*'");
        public static readonly string QuotedFragment = string.Format(R.Q(@"{0}|(?:[^\s,\|'""]|{0})+"), QuotedString);
        public static readonly string QuotedAssignFragment = string.Format(R.Q(@"{0}|(?:[^\s\|'""]|{0})+"), QuotedString);
        public static readonly string StrictQuotedFragment = R.Q(@"""[^""]+""|'[^']+'|[^\s\|\:\,]+");
        public static readonly string FirstFilterArgument = string.Format(R.Q(@"{0}(?:{1})"), FilterArgumentSeparator, StrictQuotedFragment);
        public static readonly string OtherFilterArgument = string.Format(R.Q(@"{0}(?:{1})"), ArgumentSeparator, StrictQuotedFragment);
        public static readonly string SpacelessFilter = string.Format(R.Q(@"^(?:'[^']+'|""[^""]+""|[^'""])*{0}(?:{1})(?:{2}(?:{3})*)?"), FilterSeparator, StrictQuotedFragment, FirstFilterArgument, OtherFilterArgument);
        public static readonly string Expression = string.Format(R.Q(@"(?:{0}(?:{1})*)"), QuotedFragment, SpacelessFilter);
        public static readonly string TagAttributes = string.Format(R.Q(@"(\w+)\s*\:\s*({0})"), QuotedFragment);
        public static readonly string AnyStartingTag = R.Q(@"\{\{|\{\%");
        public static readonly string PartialTemplateParser = string.Format(R.Q(@"{0}.*?{1}|{2}.*?{3}"), TagStart, TagEnd, VariableStart, VariableIncompleteEnd);
        public static readonly string TemplateParser = string.Format(R.Q(@"({0}|{1})"), PartialTemplateParser, AnyStartingTag);
        public static readonly string VariableParser = string.Format(R.Q(@"\[[^\]]+\]|{0}+\??"), VariableSegment);
        public static readonly string LiteralShorthand = R.Q(@"^(?:\{\{\{\s?)(.*?)(?:\s*\}\}\})$");
        public static readonly string CommentShorthand = R.Q(@"^(?:\{\s?\#\s?)(.*?)(?:\s*\#\s?\})$");

Answer 1

This is not a regular expression – it is a format string, as this is a call to string.Format .

This simply formats the string and places the value of the regex variable (or rather the result of calling ToString() on it) in place of the {0}.

The result is the string "(?-mix:<whatever regex.ToString() is>)".

This string looks like it could be a regular expression, and would turn off a few modifiers (so this would be case sensitive, ^ and $ match start and end of line only and free spacing mode is off). See Regular Expression Advanced Syntax Reference on http://www.regular-expressions.info.

So the above would match regex with those options off.