templated typedef;

[Stewbond]

I have a 1st order RC low-pass filter. It's implemented as a class called [/code]Filt[/code], and is defined as:

template <class T> 
class Filt {/*...*/};

That name was chosen because the colloquial phrase "I need to filter this" tends to refer to an RC low-pass filter.

Now if someone is looking for a low-pass filter in my library, they will only find Filt which they may not recognize as a low-pass filter, so I want to typedef this to simply give it another alias.

Unfortunately the template is getting in my way:

1 2 3 4 5 6 7 8 9 10

typedef Filt LowPass; typedef Filt<> LowPass; typedef Filt<> LowPass<>; template <typename T> typedef Filt<T> LowPass; typedef Filt<double> LowPass;

error C2955: 'sim::Filt' : use of class template requires template argument list error C2976: 'sim::Filt' : too few template arguments error C2143: syntax error : missing ';' before '<' error C2823: a typedef template is illegal OK

Is there a way to do this? I suppose inheritance would work instead but that requires extra code for the constructor and operator functions.

[guestgulkan]

If I get what you are trying to do - then you will find trying to typedef
a generic template is problematic/impossible.

So in C++11 you can use the using declaration like this:

template <typename T>
using MyFilter = Filt<T>; //now MyFilter is a typedef for  Filt 

You can also use using in this manner where previously you would
have used the keyword typedef.

template <class T>
class Filt {/*...*/};

/*typedef Filt LowPass;

typedef Filt<> LowPass;

typedef Filt<> LowPass<>;

template <typename T>
typedef Filt<T> LowPass;

typedef Filt<double> LowPass;*/


template <typename T>
using MyFilter = Filt<T>;

using MyFilter_Int = MyFilter<int>;


int main()
{

    MyFilter_Int mfi;

}

[JLBorges]

http://www.stroustrup.com/C++11FAQ.html#template-alias

[Stewbond]

Thanks guys.