Overload Resolution and Optional Arguments in C# 4

Posted by Dale McCoy on Stack Overflow See other posts from Stack Overflow or by Dale McCoy
Published on 2010-06-17T13:16:24Z Indexed on 2010/06/17 13:33 UTC
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overload-resolution

I am working with some code that has seven overloads of a function TraceWrite:

void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, string Data = "");
void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, bool LogToFileOnly, string Data = "");
void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, string PieceID, string Data = "");
void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, LogWindowCommandENUM LogWindowCommand, string Data = "");
void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, bool UserMessage, int UserMessagePercent, string Data = "");
void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, string PieceID, LogWindowCommandENUM LogWindowCommand, string Data = "");
void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, LogWindowCommandENUM LogWindowCommand, bool UserMessage, int UserMessagePercent, string Data = "");

(All public static, namespacing noise elided above and throughout.)

So, with that background:
1) Elsewhere, I call TraceWrite with four arguments: string, LogLevelENUM, string, bool, and I get the following errors:

error CS1502: The best overloaded method match for 'TraceWrite(string, LogLevelENUM, string, string)' has some invalid arguments
error CS1503: Argument '4': cannot convert from 'bool' to 'string'

Why doesn't this call resolve to the second overload? (TraceWrite(string, LogLevelENUM, string, bool, string = ""))

2) If I were to call TraceWrite with string, LogLevelENUM, string, string, which overload would be called? The first or the third? And why?

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