On Sun, Feb 28, 2016 at 6:49 PM, Jonathan Goldfarb <[email protected]> wrote:
> I realize now I may have been misunderstanding
> http://docs.julialang.org/en/release-0.4/manual/performance-tips/#avoid-containers-with-abstract-type-parameters
> for a long time... Is the recommendation there only related to parameterized
> types, or any user defined type? My specific question, in the latter case,
> is the following
It's about typed slot (i.e. container) in general and has nothing to
do with type parameters. using a `TypeA{AbstractType}` won't cause any
performance problem as long as you are not using the `AbstractType` as
one of the field type. OTOH, having a abstract type field will cause
any use of the field to be type unstable, no matter whether the type
is parametrized or not.
>
> Since Function is an abstract type after
> https://github.com/JuliaLang/julia/pull/13412#issuecomment-175200009 what is
The `Function` type is special in the sense that it is always
"abstract" since it never has the information for type inference when
you want to call the function. (If you are just passing functions
around without calling it then yes, `Function` was a leaftype and was
type stable)
> the recommended way to have e.g.
> immutable J
> a::Function
> b::Function
> end
If you want to specialized on the actual function called, use
```
immutable J{F1,F2}
a::F1
b::F2
end
```
Otherwise, keeping it like this shouldn't cause any performance issue
compare to 0.3 and 0.4 due to the reason mentioned above.
> be used in a performant way? Evidently, we should not form e.g. an
> Array{Function, 1}, but would using types like this in code give similarly
> poor performance?
See also my summary in https://github.com/JuliaLang/julia/issues/13984
>
> Thanks,
> Max
