In C# I sometimes wish I could make special methods for certain "instantiations" of generic classes.

UPDATE: The following code is just a dumb example of a more abstract problem - don't focus too much on time series, just the principles of "adding extra methods" for certain T.

Example:

class Timeseries<T> 
{ 
    ...
    TimeSeries<T> Slice(...) { ... }
}

In the case where T is double, I would like some extra methods, like Integrate(), Interpolate() and so on that make only sense for double, because I need to do arithmetic on them.

There are several ways to do this, but I cannot find one that I'm satisfied with.

1. Inherit into a special class

class TimeseriesDouble : Timeseries<double>
{ 
    double Interpolate(...) { ... }
    ...
}

cons: TimeseriesDouble.Slice() will return a new Timeseries<double> object, now missing my special methods.

2. External methods

public static double Interpolate(Timeseries<double> ts, ...) { ... }

cons: Breaks with OO principles. And I don't want to put my methods away. Also, the methods might need private/protected state.

3. Extension methods

Same as 2, just with a nicer calling syntax.

4. Common base class

class TimeSeries_base { ... }
class TimeSeries<T> : TimeSeries_base { .. typesafe versions of methods .. }
class TimeSeriesDouble : TimeSeries_base { .. typesafe versions of methods .. }

cons: too much duplication of things from TimeSeries_base into the two subclasses. The base class might become just a place holder for utility functions for the sub classes.

pro:

c# .net design-patterns generics
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