C# 可选参数或方法重载？

Question

<分区>

Answer 1

可选参数很好，但应该在有意义的时候使用。可选参数通常会混淆方法的意图——如果有另一种选择，我会倾向于选择另一种方法。

部分需要可选参数和命名参数是因为 COM 允许可选参数和名称参数:

MSDN

Some APIs, most notably COM interfaces such as the Office automation APIs, are written specifically with named and optional parameters in mind. Up until now it has been very painful to call into these APIs from C#, with sometimes as many as thirty arguments having to be explicitly passed, most of which have reasonable default values and could be omitted.

来自 forums.asp.net 的 SomeNewKid 简明扼要地说:

http://forums.asp.net/t/386604.aspx/1

...overloaded methods are generally preferable to optional parameters. Why? To keep each of your methods clear in purpose. That is, each method should do one thing well. As soon as you introduce optional parameters, you are diluting the cleanliness of that method, and introducing branching logic that is probably best kept out of a method. This clarity of purpose becomes even more important when you start using inheritance. If you override a method that has one or more optional parameters, they become harder to work with. So, I'd suggest that for anything other than quick and dirty classes, you use overloading in preference to optional parameters.

请记住，可选参数是一种语法糖:

反射器 C#:

public class Class1
{
    // Methods
    public Class1()
    {
        this.Method1("3", "23");
    }

    public void Method1(string one, [Optional, DefaultParameterValue("23")] string two)
    {
    }
}

IL:

.class public auto ansi beforefieldinit Class1
    extends [mscorlib]System.Object
{
    .method public hidebysig specialname rtspecialname instance void .ctor() cil managed
    {
        .maxstack 8
        L_0000: ldarg.0 
        L_0001: call instance void [mscorlib]System.Object::.ctor()
        L_0006: nop 
        L_0007: nop 
        L_0008: ldarg.0 
        L_0009: ldstr "3"
        L_000e: ldstr "23"
        L_0013: call instance void WebApplication1.Class1::Method1(string, string)
        L_0018: nop 
        L_0019: nop 
        L_001a: ret 
    }

    .method public hidebysig instance void Method1(string one, [opt] string two) cil managed
    {
        .param [2] = string('23')
        .maxstack 8
        L_0000: nop 
        L_0001: ret 
    }

}