Limiting C++ templates to primitive types

Question

I have a class that is basically a wrapper around a double that allows its value to be forced to a static value:

class ModelParameter
{
    protected:
        double val;
        bool isForced;
        double forcedVal;

    public:
        ModelParameter(void);
        ModelParameter(double value);
        double getValue(void);
        void setValue(double value);
        bool getIsForced(void);
        void forceValue(double value);
        void unforceValue(void);
};

But I want to be able to use it for any primitive types, not just doubles. If I redefine it like so:

template <class T>
class ModelParameter
{
    protected:
        T val;
        bool isForced;
        T forcedVal;

    public:
        ModelParameter(void);
        ModelParameter(T value);
        T getValue(void);
        void setValue(T value);
        bool getIsForced(void);
        void forceValue(T value);
        void unforceValue(void);
};

This would mean that any type could be used regardless if it is primitive or not. Is there any way I can restrict the types used in the template to use only primitive types?

You could borrow ideas from here: http://stackoverflow.com/questions/580922/identifying-primitive-types-in-templates?rq=1 — dutt, Dec 05 '13 at 16:19

Benjamin Lindley · Accepted Answer · 2013-12-05T16:27:51.810

18

(note: requires C++11)

#include <type_traits>

template <class T>
class ModelParameter
{
    static_assert(std::is_fundamental<T>::value, "error message");
    ...
};

But why would you want to do this?

edited Dec 05 '13 at 16:27

answered Dec 05 '13 at 16:22

Benjamin Lindley

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This is going to be used in a spacecraft simulation and one of the requirements is that all parameters in a model shall be forcible so that one can easily simulate failures (for example forcing a measured temperature to zero or forcing the deployment angle of the solar array to a fixed value). These parameters will all be primitive types, hence the reason I want to restrict the types used in the template. – rozzy Dec 06 '13 at 09:17
Also, I used std::is_arithmetic instead of std::is_fundamental as I did not want to allow void and nullptr_t types – rozzy Dec 06 '13 at 10:35
@aero117: So, you don't want to allow someone to use an extended numeric type, like a 1024 bit floating point, or an unbounded rational number? – Benjamin Lindley Dec 06 '13 at 13:42

score 7 · Answer 2 · answered Dec 05 '13 at 16:24

One way is explicit instantiation for your intended types. Move all implementations into the .cpp file and instantiate for those type:

.cpp file:

...

Definitions and implementation

....

class ModelParameter<float>;
class ModelParameter<int>;

...

Then, it just works for those types.

Limiting C++ templates to primitive types

2 Answers2

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