New concrete number type

General Usage
21

Thanks @johnmyleswhite . It’s clear from the comments above that this is more hassle than it’s worth for my case. All I want is to enforce the bounds on assignment. I understand @carstenbauer 's point, but that’s not a constraint for what I have in mind.

Thanks for the reference to refinement type: it’s helpful to know the right terminology when searching.

22

@carstenbauer You’re right: it’s the wrong reference. You’re making a good point, just not one that is relevant for what I have in mind. I should have been clearer.

23

You don’t need that. The error will be thrown when setindex! tries to convert to the correct element type.

1 Like
24

Assignment in julia is not like C++ where you can overload it.
Let’s say you run ptot = p1 + p2. If you want an error when ptot is greater than 1 you need to do the check by coding it in the + method that actually get used there.
Also mathematically, a sum of probabilities is not always a probability and can be greater than 1 like @carstenbauer noted.

1 Like
25

I think the right check should happen on construction/conversion, not necessarily by each method, like +.

I agree that checking on assignment doesn’t make sense.

1 Like
26

Yeah, construction/conversion.

27

If this is all you want, you should copy the example of Float16 instead: julia/boot.jl at 66c9f6a9b58130d35fa9cf10a7e16daf5847e575 · JuliaLang/julia · GitHub

But it doesn’t seem like it’s true that you want only this: it sounds like you want “all existing methods for Float64, except for the constructor”, which is kind of the mirror image of creating a new primitive type.

1 Like
28

Oh yes, it doesn’t need to be on the method because you will call the constructor that does the check itself.

29

Thanks @johnmyleswhite . I’ll have a look.

But yes, I want all methods to behave exactly as though they are floats except the constructor which should do bounds checking.

30

Perhaps it’s easier to make a function that looks like a constructor and makes “Probability” objects that are really Float64 objects?

julia> function Probability(x::Float64)
       if x < 0.0 || x > 1.0
       error("Invalid probability")
       end
       x
       end
Probability (generic function with 1 method)

julia> Probability(0.5)
0.5

julia> Probability(1.5)
ERROR: Invalid probability
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:33
 [2] Probability(x::Float64)
   @ Main ./REPL[1]:3
 [3] top-level scope
   @ REPL[3]:1
2 Likes
31

Thanks @johnmyleswhite .

1 Like