重载解析和C＃4中的可选参数 [英] Overload Resolution and Optional Parameters in C# 4

问题描述

我与有七个重载函数 TraceWrite 的一些代码工作：

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 = "");

（所有公共静态，噪音命名空间上面的省略和整个。）结果

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

所以，与背景：结果
1）在其他地方，我称之为 TraceWrite 用四个参数：字符串，LogLevelENUM，字符串，布尔，我也得到了以下错误：

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'

为什么没有这个调用决心第二超载？ （ TraceWrite（字符串，LogLevelENUM，字符串，布尔，字符串=））

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

2）如果我是调用 TraceWrite 与字符串，LogLevelENUM，字符串，字符串，其中超载会叫什么名字？第一或第三？为什么？

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

推荐答案

，编译器会选择超载＃1，因为它有参数的数量和签名完全匹配。

The compiler will choose overload #1 because it has an exact match for the number of parameters and the signature.

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