Invalid object type

[Gemorroj]

If the object inherits object Decimal, methods from* return the wrong object.

example: https://gist.github.com/Gemorroj/f1a5ccc98d90615a3bf754b839b04300
I think #32 this is resolve problem

[castarco]

This library has many problems and shortcomings due to bad design decisions, but the use case that you are explaining here is not a good example of such problems. In fact, there are far better ways to represent prices (through composition, not through inheritance).