这个奇怪的 StringBuilder 在 ANTLR 生成的代码中做什么？

Question

I'm trying to learn how to use Antlr4 in Unity. I saw code in class ActionLexer from other program

private static string _serializeATN()
{
StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.Append("\u0003а훑舆괭䐗껱趀ꫝ\u0002\u000e");
        stringBuilder.Append("\u00a0\b\u0001\u0004\u0002\t\u0002\u0004\u0003\t\u0003\u0004\u0004\t\u0004\u0004\u0005\t\u0005\u0004\u0006");
        stringBuilder.Append("\t\u0006\u0004\a\t\a\u0004\b\t\b\u0004\t\t\t\u0004\n\t\n\u0004\v\t\v\u0004\f\t\f");
        stringBuilder.Append("\u0004\r\t\r\u0004\u000e\t\u000e\u0004\u000f\t\u000f\u0004\u0010\t\u0010\u0004\u0011\t\u0011\u0004");
        stringBuilder.Append("\u0012\t\u0012\u0003\u0002\u0003\u0002\u0003\u0003\u0003\u0003\u0003\u0004\u0003\u0004\u0003\u0005\u0003\u0005\u0003");
        stringBuilder.Append("\u0006\u0003\u0006\u0003\a\u0003\a\u0003\b\u0003\b\u0003\b\u0003\b\u0003\b\u0003\b\u0003\b\u0003\b");   
             ...
return stringBuilder.ToString();

}

and then I copyed that code in my unity and debug it. the result is strange string.

+       stringBuilder   "а훑舆괭䐗껱趀ꫝ \b\t\t\t\t\t\a\t\a\b\t\b\t\t\t\n\t\n\v\t\v\f\t\f" System.Text.StringBuilder

I want to know why that happen. what is role for this function?

Answer 1

The ATN is the internal.network (Augmented Transition Network) used by the ATN interpreter to execute the parser + lexer state machines. This structure is generated by ANTLR out of the grammar it was given and is at the heart of the entire machinery of the ANTLR implementation.

The generated parser and lexers need their ATN to work properly. But since the generated files are text it was necessary to serialise the generated.network into a text string, to be able to write it to the generated files. This string is then de-serialised on startup of the parsing application to regenerate the original ATN in memory. So in short: it's not text per se, but binary data stored as text.

The ATN belongs to the internals of the parser/lexer implementation and you can safely ignore it for most purposes.

Answer 2

You are looking at non-printable unicode characters. Quite what they are doing here is a bit of mystery.

• is ASCII code 2 (STX)
• is ASCII code 3 (ETX)
• \t is a tab character
• \a is a Line Feed character

https://www.rapidtables.com/code/text/ascii-table.html