Wiki page "Supported types" does not mention ConcatenatedString

[kpreisser]

Hi,

the Wiki page Supported types shows which JS type maps to which .NET type. The table contains an entry for JS type string which maps to .NET type System.String.

However, I found that sometimes Jurassic supplies an Jurassic.ConcatenatedString instead of a regular System.String when calling a function, if the JS string has been constructed using the + operator. E.g.:

    ScriptEngine engine = new ScriptEngine();
    engine.SetGlobalFunction("myFunc", new Action<object>(arg =>
    {
        Console.WriteLine(arg.GetType() + ": " + arg.ToString());
    }));

    engine.Execute(@"
myFunc('abc');
myFunc('ab' + 'c');
");

displays:

System.String: abc
Jurassic.ConcatenatedString: abc

I think this could be added to the wiki page to avoid confusion. (When the .NET declares the parameter as string Jurassic automatically converts it to a string, but not when declaring it as object which is sometimes needed if the function should allow parameters of different types.)

Should I add this to the Wiki page? Thanks!

[paulbartrum]

Yes, you're right, this is a bit of a trap. ConcatenatedString is intended as a performance optimization, for when you are concatenating in a loop, like this:

s = "start";
for (var i; i < 15; i ++) { s += ", " + i; }
// do something with s

This results in only three strings (and a StringBuilder) being created, rather than the naïve approach, which creates ~30.

Rather than changing the docs, I would rather treat this as a bug and convert ConcatenatedString to a regular string before passing it to the user-defined function.

For now, you can use TypeUtilities.TypeOf() and TypeConverter.ToString() to deal with strings & concatenated strings in a generic way. (There's also TypeUtilities.IsString() but that's internal...)