Pass RegexMatch to a function?

[Jonathan M Davis via Digitalmars-d-learn]

On Tuesday, August 09, 2016 01:07:53 Gerald via Digitalmars-d-learn wrote:
> I have a RegexMatch that I want to pass to a function that takes
> the match and replaces various tokens in a string with the match
> and/or individual groups of the match. I'm struggling to figure
> out how to pass a RegexMatch to a function, right now I have code
> like the follows:
>
> RegexMatch regexMatch = matchAll(urlMatch.match,
> regex(tr.pattern, tr.caseless?"i":""));
> string command = replaceMatchTokens(urlMatch.match, regexMatch);
>
> ...
>
> string replaceMatchTokens(string tokenizedText, ref RegexMatch
> match) {
>      string result = tokenizedText.replace("$0", match.match);
>
>      int i = 0;
>      foreach(group; match.captures) {
>          result = result.replace("$" ~ to!string(i), group);
>          i++;
>      }
>      return result;
> }
>
> When I try to compile this, it fails with the follow on the line
> where replaceMatchTokens is declared:
>
> Error: struct std.regex.RegexMatch(R, alias Engine =
> ThompsonMatcher) if (isSomeString!R) is used as a type
>
> I've also tried declaring it as follows:
>
> string replaceMatchTokens(string tokenizedText, ref
> RegexMatch!(string, ThompsonMatcher) match) {
>
> With the following errors:
>
> source/gx/terminix/terminal/terminal.d(1273,28): Error: struct
> std.regex.RegexMatch(R, alias Engine = ThompsonMatcher) if
> (isSomeString!R) is used as a type
> source/gx/terminix/terminal/terminal.d(2701,54): Error: template
> std.regex.match cannot deduce function from argument types
> !()(RegexMatch!(string, ThompsonMatcher)), candidates are:
> /usr/include/dlang/dmd/std/regex/package.d(777,13):
> std.regex.match(R, RegEx)(R input, RegEx re) if (isSomeString!R
> && is(RegEx == Regex!(BasicElementOf!R)))
> /usr/include/dlang/dmd/std/regex/package.d(785,13):
> std.regex.match(R, String)(R input, String re) if (isSomeString!R
> && isSomeString!String)
> /usr/include/dlang/dmd/std/regex/package.d(792,13):
> std.regex.match(R, RegEx)(R input, RegEx re) if (isSomeString!R
> && is(RegEx == StaticRegex!(BasicElementOf!R)))

RegexMatch is a templated type, so if you type RegexMatch, you're not
providing an actual type - just the name of the template used to generate a
type. For instance, if you have

struct S(T)
{
    T member;
}

S would be meaningless in most cases. It would be instantiations of S such
as S!int or S!string which would actually be types. Almost always, the
solution when dealing with templated types is to templatize your function
(you can specify the exact instantiation you're using, but that can get
pretty ugly. In this case, what you probably want is something like

string replaceMatchTokens(RM)(string tokenizedText, RM match)
    if(std.traits.isInstanceOf(RegexMatch, RM))
{
    ...
}

- Jonathan M Davis