Re: [boost] Boost Units library preview

From: Andy Little (andy_at_[hidden])
Date: 2006-08-21 18:21:32

"Andy Little" <andy_at_[hidden]> wrote in message 
news:ecda4t$hjc$1_at_sea.gmane.org...
>
> "Deane Yang" <deane_yang_at_[hidden]> wrote in message
> news:ecd87h$brg$1_at_sea.gmane.org...
>> Eric Lemings wrote:
>>>> This brings up a good question.  Say you have two objects:
>>>>
>>>> meters m = 1;
>>>> feet f = 2;
>>>>
>>>> What is the type (or unit) of the following expression?
>>>>
>>> m + f;
>>>
>>
>> I apologize for repeating myself, but I want this to fail to compile. I
>> do not want implicit conversion of units. I believe I am not completely
>> alone in this view.
>
> Personally I love implicit unit conversions. :-)
> I can add a function to prevent them, but you will have to apply that
> explicitly:
>
> T b = no_cast(a);
>
> or some such.
>
> How's that?
>
> regards
> Andy Little

For addition you would need to do this:

nocast(a) + nocast(b);

for multiplication

nocast(a) * nocast(b);

You could make this a general purpose utility:

template <typename T>
struct no_caster{
T t;
/*...*/
};

template <typename T1, typename T2>
typename boost:enable_if<
    boost::is_same<T1, T2>,T1
>::type

 operator Op (nocaster<T1> ,nocaster<T2>);

regards
Andy Little