如何在C＃中将正则表达式与带有括号的模式匹配

Question

Background: I'm doing some complicated code generation that requires me to extract the methods within a C# interface file. I cannot simply use reflection because this code will feed a T4 template which will not have the compiled code to reflect upon. Thus I am attempting parsing. I can easily make my own parser, but it would be nice if there was a regular expression solution.

Question: Is-there/What regex pattern would match the method declarations (including the return types and parameters) of the string below using C#'s Regular Expressions library?

    string testing = @"
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;

    namespace ConsoleApplication1
    {
        public interface Service
        {
            int Test1(int a);

            int Test2(int a, int b);

            int Test3(
                int a,
                int b);

            int Test4(out int a);
        }
    }
    ";

The regex pattern I desire should make four matches:

1. "int Test1(int a);"
2. "int Test2(int a, int b);"
3. "int Test3( int a, int b);" [note: #3 would be multi-line]
4. "int Test4(out int a);"

Solution Attempt: Here is possibly the closest I have come to a regex solution thus far:

string WhiteSpacePattern = @"\s+";
string PossibleWhiteSpacePattern = @"\s*";
string CsharpWordPattern = @"[a-zA-Z_]+";
string ParenthesesPattern = @"[(][\s\S]*?[)]";

string DoubleCsharpWordPattern = CsharpWordPattern + WhiteSpacePattern + CsharpWordPattern;
string MethodDeclarationPattern =
    DoubleCsharpWordPattern +
    PossibleWhiteSpacePattern +
    ParenthesesPattern;

Pattern usage example:

MatchCollection tests = Regex.Matches(testing, MethodDeclarationPattern);

The individual patterns work perfectly (CsharpWordPattern, ParenthesesPattern, WhiteSpacePattern, and PossibleWhiteSpacePattern). However, when I put them altogether into a single pattern (MethodDeclarationPattern), the full pattern is failing.

How does MethodDeclarationPattern or my usage example need to be altered so that it will start matching the method declarations in the interface code?

Answer 1

To match literal parens, escape them with backslashes:

string ParenthesesPattern = @"\([\s\S]*?\)";

That regex snippet matches a matched pair of parentheses, with optional whitespace between them. You're putting it at the end of your overall regex.

Your complete concatenated regex looks like this:

[a-zA-Z_]+\s+[a-zA-Z_]+\s*[(][\s\S]*?[)]

Identifier, space, identifier, open paren, space, close paren.

For that to match, the method declaration will have to look like this:

"int foo ()"

I believe you'll have better success with something like this:

string openParenPattern = @"\([\s\S]*?";
string closeParenPattern = @"[\s\S]*?\)";

What you really need, conceptually, is this (leaving out space -- no need to clutter it up with that):

1. identifier
2. identifier
3. open paren
4. ((ref|out)? identifier identifier comma)*
5. ((ref|out)? identifier identifier)?
6. close paren

You know all the syntax for that, I think. You'll have nested groups. Looking at it, I'm really starting to warm up to your idea of putting sub-regexes in string variables and then concatenating them.

The following code matches all four method declarations in your test string:

//  This has one bug: It matches "int foo(int a,)"
//  Somebody good with regexes could fix that. 
var methodPattern =
    //  return type
        identPattern + spacePattern
    //  method name
    + identPattern + spacePattern
    //  open paren
    + openParenPattern + spacePattern
    //  Zero or more parameters followed by commas
    + "(" + paramPattern + spacePattern + "," + spacePattern + ")*" + spacePattern
    //  Final (or only) parameter not followed by a comma
    + "(" + paramPattern + spacePattern + ")?" + spacePattern
    //  Close paren
    + closeParenPattern;