如何使索引的类型 [英] How to make types for indexing

问题描述

我有类似的：

数组定义：

array<array<Value, N_FOO_PER_BAR>, N_BAR> arr;

存取功能：

Value getFoo(int barIdx, int fooIdx){
  return arr[barIdx][fooIdx];
}

For-loop：

for(int i = 0; i < N_BAR; i ++){
  for(int j = 0; j < N_FOO_PER_BAR; j ++){
    arr[i][j].doSomething();
  }
} 

问题：使用 getFoo（...）时，foo和bar很容易混淆。

Problem: Indices for foo and bar can easily get mixed up when using getFoo(...).

一个类型 BarIdx 和 FooIdx ，然后编译器会在我混淆时提出抱怨。

I would like to define a type BarIdx and FooIdx and then the compiler should complain when I mix them up.

然后，访问函数将如下所示：

The access function would then look like:

function getFoo(BadIdx barIdx, FooIdx fooIdx){
  return arr[barIdx][fooIdx];
}

for-loop可能如下所示：

The for-loop could look like:

for(BarIdx i = 0; i < N_BAR; i ++){
  for(FooIdx j = 0; j < N_FOO_PER_BAR; j ++){
    arr[i][j].doSomething();
  }
} 

所以我在寻找如何定义一个类型（a）将在错误的位置使用时发出警告/错误，但是（b）仍然尽可能地表现为整数，对于使用[]的for循环和数组访问。这应该也适用于CUDA，所以我宁愿使用简单的语言结构，而不是一个完美的解决方案。

So I'm looking how to define a type which (a) will issue a warning/error when used at the wrong place but (b) still behaves as much as an integer as possible, for for loop and array access with []. This should also work on CUDA, so I would prefer to use simple language constructs rather than a perfect solution.

推荐答案

这样做是因为您不能简单地继承自int 在C ++中，所以你需要提供一个包装器，它不仅隐式地转换和从 int ，而且还提供了所有必要的操作符，以便你可以做像： p>

The difficulty with doing this is that you can't simply inherit from int in C++, so you need to provide a wrapper which not only implicitly converts to and from int, but also provides all the necessary operators so that you can do things like:

BarIdx a = 0;
++a;

您可能希望从这样简单的开始：

You might want to start with something simple like this:

template <typename T>
class IntegralWrapper {
    T value;
public:
    typedef T value_type;
    IntegralWrapper() :value() {}
    IntegralWrapper(T v) :value(v) {}
    operator T() const { return value; }
};

然后添加您以后需要的任何运算符。然后你可以这样定义你的索引类：

Then add any operators you need later. You would then define your index classes like this:

class BarIdx : public IntegralWrapper<int> {};
class FooIdx : public IntegralWrapper<int> {};

或者，这里是一个看起来相当完整的整体封装解决方案取自这个问题，你可能会使用。

Alternatively, here is a seemingly pretty complete integral wrapper solution taken from this question which you could probably use.

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