通用Func中的可选参数. [英] Optional arguments in a generic Func<>

问题描述

我在程序集中具有以下方法:

I have the following method in an assembly:

public string dostuff(string foo, object bar = null) { /* ... */ }

我将其用作回调，因此对它的引用将传递给另一个程序集，例如:

I use it as a callback, so a reference to it is passed to another assembly as such:

Func<string, object, string> dostuff

现在以原始形式，无需指定第二个参数(默认为null)就可以调用它.但是，当我将它用作第二个程序集中的回调时，必须指定第二个参数.

Now in the original form, I can call it without specifying that second argument, which defaults to null. But when I use it as a callback in that second assembly, I must specify that second argument.

什么语法允许我忽略第二个参数?

推荐答案

您将需要创建一个新方法，该方法仅接受一个参数，并传递第二个参数的默认值.如果需要，您可以使用lambda来执行此操作，而不是创建一个新的命名方法:

You'll need to create a new method that accepts only one argument, and that passes the default value for the second argument. You could do this with a lambda, rather than creating a new named method, if you wanted:

Func<string, string> doStuffDelegate = s => dostuff(s);

另一种选择是使用签名具有可选的第二个参数的委托，而不是使用Func，在这种情况下，方法的签名将匹配:

The other option would be to use a delegate who's signature has an optional second argument, instead of using Func, in which case your method's signature would match:

public delegate string Foo(string foo, object bar = null);

您可以直接将dostuff分配给Foo类型的委托，并且在调用该委托时只能指定一个参数.

You could assign dostuff to a delegate of type Foo directly, and you would be able to specify only a single parameter when invoking that delegate.

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