Question

I’ve just installed VS2008 and have run into a problem that I’m sure can be solved with either lambda’s or delegates (or a combination!).

    private string ReadData(TcpClient s, string terminator)
    {
        // Reads a byte steam into a string builder until either data is unavailable or the terminator has not been reached
        var sb = new StringBuilder();
        do
        {
            var numBytesRead = s.GetStream().Read(byteBuff, 0, byteBuff.Length);
            sb.AppendFormat("{0}", Encoding.ASCII.GetString(byteBuff, 0, numBytesRead));
        } while (s.GetStream().DataAvailable && !sb.ToString().Contains(terminator));

        return sb.ToString();
    }

The problem is, sometimes I need to check if the string contains either of two different values. Sometimes I may need to check it for three values.

So what I propose, is to change ” !sb.ToString().Contains(terminator)” to a function that is passed into the method.

I could write my different functions such as:

private bool compare1(string s, string t) {
    return s.contains(t)
}

private bool compare2(string s, string t1, string t2) {
    return (s.compare(t1) or s.compare(t2)
}

// etc...

Then when I want to compare with 3 different values, create a delegate to one of these functions, then pass that to the ReadData() method.

I’m very clueless when it comes to delegates, and I’m not sure if this seems like the right place for a lambda but something is telling me it is.

The calling code is this:

            // Enter username .
        if (HasData(s,"login:"))
            SendData(s, switchUser + TelnetHelper.CRLF);

HasData is identical to ReadData, but returns a bool instead of a string (which I’d also like to factor out into one method using some trickery – but that’s a secondary question – feel free to answer that though.

Just for reference:

     private bool HasData(TcpClient s, string terminator)
    {
        // Reads a byte steam into a string builder until either data is unavailable or the terminator has not been reached
        var sb = new StringBuilder();
        do
        {
            var numBytesRead = s.GetStream().Read(byteBuff, 0, byteBuff.Length);
            sb.AppendFormat("{0}", Encoding.ASCII.GetString(byteBuff, 0, numBytesRead));
        } while (s.GetStream().DataAvailable && !sb.ToString().Contains(terminator));

        return sb.ToString().Contains(terminator);
    }

Answer 1

It sounds like you’re looking for a predicate function. Instead of hard coding the check, take a delegate as a parameter than can do the check

    private string ReadData(TcpClient s, Func<string,bool> predicate)
    {
        // Reads a byte steam into a string builder until either data is unavailable or the terminator has not been reached
        var sb = new StringBuilder();
        do
        {
            var numBytesRead = s.GetStream().Read(byteBuff, 0, byteBuff.Length);
            sb.AppendFormat("{0}", Encoding.ASCII.GetString(byteBuff, 0, numBytesRead));
        } while (s.GetStream().DataAvailable && !predicate(sb));

        return sb.ToString();
    }

Then you can create several wrappers which just create the appropriate delegate and pass it down

public bool HasData(TcpClient c, string terminator) {
  return HasData(c, (s) => s.Contains(terminator));
}

public bool HasData(TcpClient c, string t1, string t2) {
  return HasData(c, (s) => s.Contains(t1) || s.Contains(t2));
}

You can even build a delegate on the fly based on arbitrary number of terminators

public bool HasData(TcpClient c, params string[] terminatorList) {
  return HasData(c, (s) => terminatorList.Where(x => s.Contains(x)).Any());
}