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F# ships with special support for a unit of measurement system, which provides static type safety while compiling down to the numeric types instead of burdening the runtime with wrapping/unwrapping operations.
Is it possible to use some of Scala’s type system magic to implement something comparable to that?
Kind of. You can encode the SI units quite easily using a type representation of integers in a tuple of exponents. See http://svn.assembla.com/svn/metascala/src/metascala/Units.scala for an example implementation.
It should also be possible to support an extensible units system if the units are encoded as a
TListof pairs of a unit type and an integer (for example,((M, _1), (S, _2))whereM <: UnitandS <: Unit). Calculating the types for quantity operations becomes a bit more complicated in this encoding.Regarding performance there will always be a memory overhead for wrapping the value in a type containing the unit information. However there is probably no performance overhead in the actual operations as all unit checking is done at compile time.