Hello Julia Users,
I have wanted to use dispatch to enable the extraction of features or
metrics. This way you can define a large collection of features that all
extend AbstractFeature, and then just run through a list of them to get
your feature vector.
One way this could be implemented is as follows:
abstract AbstractFeature
extract(f::AbstractFeature, ::State) = error("extract not implemented for
AbstractFeature $f)
type FeatureA <: AbstractFeature end
extract(f::FeatureA, s::State) = 1.0
type FeatureB <: AbstractFeature end
extract(f::FeatureB, s::State) = 2.0
...
This is great in theory, but in practice you end up having to iterate over
an abstract array, ::Vector{AbstractFeature}, which is slow.
Other options include only having one Feature type:
type Feature
id::Int
end
function extract(f::Feature, s::State)
if f.id == 1
# code for feature 1...
elseif f.id == 2
# code for feature 2...
elseif ...
end
end
You lose the ability to define Features with different internal fields /
parameters.
I was thinking you can also dispatch on the internal id value. Would this
work?
type Feature
id::Int
end
extract(::Type{Val{1}}, s::State) = 1.0
extract(::Type{Val{2}}, s::State) = 2.0
This is a little annoying because the ids are non-intuitive and you have to
ensure there is no collision when you define new ones.
Any ideas / recommendations?
