限制 C++ 中值类型的范围

2021-12-13 00:00:00 templates c++

假设我有一个 LimitedValue 类，它保存一个值，并在 int 类型min"和max"上参数化.您可以将它用作保存只能在特定范围内的值的容器.你可以这样使用它:

Suppose I have a LimitedValue class which holds a value, and is parameterized on int types 'min' and 'max'. You'd use it as a container for holding values which can only be in a certain range. You could use it such:

LimitedValue< float, 0, 360 > someAngle( 45.0 );
someTrigFunction( someAngle );

这样 'someTrigFunction' 就知道它保证提供一个有效的输入(如果参数无效，构造函数会抛出异常).

so that 'someTrigFunction' knows that it is guaranteed to be supplied a valid input (The constructor would throw an exception if the parameter is invalid).

不过，复制构造和赋值仅限于完全相同的类型.我希望能够做到:

Copy-construction and assignment are limited to exactly equal types, though. I'd like to be able to do:

LimitedValue< float, 0, 90 > smallAngle( 45.0 );
LimitedValue< float, 0, 360 > anyAngle( smallAngle );

并在编译时检查该操作，因此下一个示例给出错误:

and have that operation checked at compile-time, so this next example gives an error:

LimitedValue< float, -90, 0 > negativeAngle( -45.0 );
LimitedValue< float, 0, 360 > postiveAngle( negativeAngle ); // ERROR!

这可能吗?有没有一些实用的方法可以做到这一点，或者有什么例子可以解决这个问题?

Is this possible? Is there some practical way of doing this, or any examples out there which approach this?

推荐答案

你可以使用模板来做到这一点――试试这样的:

You can do this using templates -- try something like this:

template< typename T, int min, int max >class LimitedValue {
   template< int min2, int max2 >LimitedValue( const LimitedValue< T, min2, max2 > &other )
   {
   static_assert( min <= min2, "Parameter minimum must be >= this minimum" );
   static_assert( max >= max2, "Parameter maximum must be <= this maximum" );

   // logic
   }
// rest of code
};

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