根据类型参数生成函数 [英] Generate functions based on type parameter

问题描述

我想为一个接受1个类型参数的类生成函数，该参数包装一个按名称值.

I would like to generate functions for a class accepting 1 type parameter, which wraps a by name value.

class C[T](_t: => T) {
    def t: T = _t
}

我想生成的函数是由T上可用的函数派生的.

The functions I would like to generate are derived by the functions available on T.

我确切想要的是获取所有可用于T的功能，以编程方式更改其合约和实施，并使它们可用于C.

What I would like exactly, is to get all the functions available for T, change their contract and implementation in a programmatic way, and make them available for C.

• 通过更改其合同，我的意思是更改其签名，以便它们返回C[R]，其中R代表原始函数的返回类型.

• By changing their contract, I mean changing their signature so they return C[R], where R stands for the return type of the original function.

通过更改其实现，我的意思是在返回结果之前将结果包装在C中.

By changing their implementation, I mean wrapping the result inside C before returning it.

例如

def +(that: Int): Int =
    this + that

将在C[Int]上以

def +(that: Int): C[Int] =
    C(this.t + that)

这样做是为了消除必须包装C内部的计算以保持其未评估状态的样板.

This would be done in order to remove the boilerplate of having to wrap inside C a computation in order to keep it non-evaluated.

例如

val c1 = new C(1)

val c2: C[Int] = C(c1.t + 1)
c2.t == 2

也可以表示为

val c2: C[Int] = c1 + 1
c2.t == 2

如何通过使用Scala 2或dotty宏来实现此目标?还是可以通过其他方式实现?

How can I achieve this by using Scala 2 or dotty macros? Or, can this be achieved in another way?

推荐答案

在您之前的或使类隐式

implicit class C[T](_t: => T) {
  def t: T = _t
}

关于宏，由于要添加定义，因此需要宏注释，而不是 def宏. Dotty没有宏注释，它只有内联宏，例如Scala 2 def宏.

Regarding macros, since you want to add definitions you would need macro annotations rather than def macros. Dotty doesn't have macro annotations, it has only inline macros like Scala 2 def macros.

宏注释也无济于事.定义类C[T]时，不知道T是什么(只有在调用站点知道)，因此不知道要添加什么方法.

And macro annotations don't help either. When you define class C[T] it's not known what T is (this will be known only at call site), so it's not known what methods to add.

Dotty也有隐式转换

Dotty has implicit conversions too

given [T] as Conversion[T, C[T]] = new C(_)
given [T] as Conversion[C[T], T] = _.t

(当前是given，以前是implicit，然后是implied，然后是delegate，当前为0.17 given，可以再次更改).

(currently it's given, formerly it was implicit, then implied, then delegate, currently in 0.17 given, this can change again).

似乎不允许Conversion[(=> T), C[T]].

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