泛型谓词的默认值作为参数 [英] Default value on generic predicate as argument

问题描述

我第一次提问:)

我需要一些方法来使用格式上的泛型定义默认谓词

I need some way to define a default predicate using a generic on the format

Func<T, bool>

然后将其用作默认参数.像这样:

and then use this as a default argument. Something like this:

public bool Broadcast(byte command, MemoryStream data, bool async, Func<T, bool> predicate = (T t) => true)

当我这样做时，我收到编译错误:

When i do this i get the compile error:

谓词"的默认参数值必须是编译时常量

Default parameter value for 'predicate' must be a compile-time constant

是否有一种流畅的方法可以做到这一点，我是否应该将谓词函数设为可空并相应地更改我的函数逻辑?

Is there a smooth way of doing this that I am missing or should a make the predicate function nullable and change my function logic accordingly?

谢谢，

推荐答案

方法参数的默认值必须是编译时常量，因为默认值实际上是由编译器复制到方法的所有调用点.

Default values for method parameters have to be compile-time constants, as the default values are actually copied to all the call sites of the method by the compiler.

你必须使用重载来做到这一点:

You have to use an overload to do this:

public bool Broadcast(byte command, MemoryStream data, bool async) {
    return Broadcast(command, data, async, t => true);
}

public bool Broadcast(byte command, MemoryStream data, bool async, Func<T, bool> predicate) {
    // ...
}

此外，在 mscorlib 中有一个特定的 Predicate 委托，您可以使用它来代替.它与 Func 的签名相同，但它明确地将其标记为一个委托，该委托决定是否对 T

Also, there is a specific Predicate<T> delegate in mscorlib which you can use instead. It's the same signature as Func<T, bool>, but it explicitly marks it as a delegate which decides whether an action is performed on instances of T

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