I think the mathematical definition of "function" is not right here,
although the ! is used to indicate a function that changes one of its
arguments elsewhere in Julia because of the drastic difference in the
properties of the scope inside perhaps another word altogether could be
used?
member lowpass (this::FilterFE1, input::Float64)
local hp = input - lp
lp = lp + g * hp
[lp, hp]
end
Ok, so does everyone from the Julia development team hate me now? hehe
On Wednesday, June 18, 2014 2:06:51 PM UTC+8, Andrew Simper wrote:
>
> I feel like I'm going round in circles here, I'm back to the old @withonly
> since using a composite type to allow mutable behaviour leads to this sort
> of thing:
>
> type FilterFE1
> lp::Float64
> g::Float64
> end
>
> function lowpass(state::FilterFE1, input::Float64)
> # pull state into local variables
> g = state.g
> lp = state.lp
>
> # now the actual code (imagine this was around 100x more complicated
> so you really don't want
> # to have state.lp and state.g everywhere since it would make the code
> unreadable
> hp = input - lp
> lp = lp + g * hp
>
> # push local variables into state
> state.lp = lp
>
> # return the low pass and high pass outputs
> [lp, hp]
> end
>
> So that is the result of a rather trivial of lowpass filter examples so
> it's gone from a very easy to understand:
>
> function lowpass(input::Float64, mutable lp::Float64, g::Float64)
> hp = input - lp
> lp += g * hp
> [lp, hp]
> end
>
> into a much more complicated and error prone beast, which will just get
> more complicated the more state there is. (ps: there is no mutable keyword,
> I just added that to make it clear the intention of this code).
>
> If there was such a macro as @withonly then it would look more like:
>
> function lowpass(state::FilterFE1, input::Float64)
> @withonly state::FilterFE1, input begin
> local hp = input - lp
> lp = lp + g * hp
> [lp, hp]
> end
> end
>
> which in is a little a lot less brittle and almost as easy to read as the
> original code, probably better again would be some kind of "withonly"
> function syntax like:
>
> thisfunction lowpass (this::FilterFE1, input::Float64)
> local hp = input - lp
> lp = lp + g * hp
> [lp, hp]
> end
>
> And inside the "thisfunction" the first parameter is like a class in c++
> where you can refer to the names of this without needing to putting "this."
> in front of them, all other arguments passed must not be a name of the this
> type, and all local variables must be declared explicitly with the "local"
> keyword.
>
