Property regexp.Callout

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Overload

Sets callout callback function.

public Action<RXCalloutData> Callout { set; }

Property Value

Action<RXCalloutData> Callback delegate (eg lambda) or null.

Remarks

Callouts can be used to:

• Track the matching progress.
• Get all instances of a group that can match multiple times.
• Evaluate and reject some matches or match parts.
• Etc. The callback function is called by IsMatch, Match, FindAll, Replace, Split and similar functions, when they reach callout points in regular expression. To insert callout points use (?C), (?C1), (?C2), (?C'name') etc or pass flag AUTO_CALLOUT to the constructor. More info in PCRE help topic pcre2callout. See also: https://www.rexegg.com/pcre-callouts.html

Examples

Track the matching progress.

var s = "text <a href='url'>link</a> text";
var rx = @"(?C1)<a (?C2)href='.+?'>(?C3)[^<]*(?C4)</a>";
var x = new regexp(rx);
x.Callout = o => { print.it(o.callout_number, o.start_match, o.current_position, s[o.start_match..o.current_position], rx.Substring(o.pattern_position, o.next_item_length)); };
print.it(x.IsMatch(s));

Track the matching progress with flag AUTO_CALLOUT.

var s = "one 'two' three";
var rx = @"'(.+?)'";
var x = new regexp(rx, RXFlags.AUTO_CALLOUT);
x.Callout = o => print.it(o.current_position, o.pattern_position, rx.Substring(o.pattern_position, o.next_item_length));
print.it(x.IsMatch(s));

Get all instances of a group that can match multiple times.

var s = "BEGIN 111 2222 333 END";
var x = new regexp(@"^(\w+) (?:(\d+) (?C1))+(\w+)$");
var a = new List<string>();
x.Callout = o => a.Add(o.LastGroupValue);
if(!x.Match(s, out var m)) { print.it("no match"); return; }
print.it(m[1]);
print.it(a); //all numbers. m[2] contains only the last number.
print.it(m[3]);

Evaluate and reject some matches or match parts. This code rejects matches longer than 5.

var s = "one 123-5 two 12-456 three 1-34 four";
var x = new regexp(@"\b\d+-\d+\b(?C1)");
x.Callout = o => { int len = o.current_position - o.start_match; /*print.it(len);*/ if(len > 5) o.Result = 1; };
print.it(x.FindAll(s, 0));