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@gregoryyoung
gregoryyoung / ProbabilityKata
Created Jun 10, 2011
Greg Young's Probability Kata
View ProbabilityKata
Value objects are an important concept in DDD. This kata is made both to learn value objects and to learn better ways of testing.
Write a probability value object. It should contain the following methods:
Probability CombinedWith(Probability)
Probability InverseOf()
Probability Either(Probability)
if you forget your probability math:
Either:P(A) + P(B) - P(A)P(B)
CombinedWith: P(A)P(B)
@gregoryyoung
gregoryyoung / ProbabilityKata2
Created Jun 10, 2011
Probability Kata part 2
View ProbabilityKata2
OK so now you have implemented the kata. Your tests should look something like this:
We can say that the tests define the object "in a calculus of itself". They are not state based tests, they define how the behaviours of the object interact with each other.
To see the real value of this let's introduce some change ... I hear real system's do this occasionally. Because this is a high performance system decimal math is too slow. You now need to use floats instead.
Need help on floating point math? Check out: http://www-users.math.umd.edu/~jkolesar/mait613/floating_point_math.pdf
You will need to use a non-exact equality... How will this change your code?
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