Using template instead of switch

Question

I want to perform a set of tests in my code that are similar but change only depending on a parameter.

I could write this using a switch statement:

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Answer 1

Building off Andrew's answer...

Note that the EnumSensorFamily family must be known at compile time. If it is not known until run time, then you'll have to write a switch to choose the template, putting you back where you started.

Another way to do this is with the Traits pattern:

template 
struct SensorTraits;

template <>
struct SensorTraits
{
    const EnumSensorFamily kFamilyID = ExpectedFam1;
};

template <>
struct SensorTraits
{
    const EnumSensorFamily kFamilyID = ExpectedFam2;
};

template <>
struct SensorTraits
{
    const EnumSensorFamily kFamilyID = ExpectedFam3;
};

template 
bool doTest(const StructSensorProposal& proposed)
{
  return (SensorTraits::kFamilyID == proposed.Fam1SensorId);
}

If you try to use doTest with a sensor family that lacks a traits specialization, you get a compile error. Also note that you never instantiate a traits object, you just use its definitions.

This lets you reuse constants, typedefs, whatever in several functions. Additionally, adding a new family does not involve combing through all the code looking for every switch statement that cares. All you have to do is create a new SensorTraits specialization.

EDIT: You can make the field dependent on the sensor family with a pointer to member:

template <>
struct SensorTraits
{
    const EnumSensorFamily kFamilyID = ExpectedFam1;
    int StructSensorProposal::*proposalField = &StructSensorProposal::fam1field;
};

// ...

template 
int getProposedField(const StructSensorProposal& proposed)
{
    return proposed.*SensorTraits::proposalField;
}

You can also put in, say, a typedef for the sensor's data type:

template <>
struct SensorTraits
{
    const EnumSensorFamily kFamilyID = ExpectedFam1;
    typedef uint16_t data_type;
    data_type StructSensorProposal::*proposalField = &StructSensorProposal::fam1field;
};

// ...

template 
SensorTraits::data_type getProposedField(const StructSensorProposal& proposed)
{
    return proposed.*SensorTraits::proposalField;
}

I haven't tested these; you might need a const or static in there.