Le mercredi 06 janvier 2016 à 13:48 +0100, Michael Krabbe Borregaard a
écrit :
> Interesting. I come from R, and one of the main advantages I feel
> Julia has is that I do not have to do any in-function testing of what
> types of arguments the user has passed into the function, generating
> error messages etc. In Julia, all of this is handled automatically if
> I specify a function argument.
Yes, that's a feature that I really appreciate too! When it is obvious
that one is expecting e.g. a Number or an AbstractString, there's no
reason not to restrict the type (both for correctness and
documentation).
> I would think the ideal way of doing it would be to specify a
> function argument with a broad type (e.g. Number) that is meaningful
> for all the operations in the function, and prevents the user from
> e.g. passing in a string and getting a weird error message, or a bool
> and getting something spurious. Unfortunately, most of my functions
> do not take simple types, they take Vectors, and a Vector{Int} does
> not inherit from a Vector{Number}! - meaning that the whole idea of
> inheritance is a bit lost for me. I guess I can do foo{T <:
> Number}(a::Vector{T}) but that goes very far from the easy non
> -specifying format that you support.
>
> In short, I am really confused about how to use types well in Julia
> functions - and I did read the style guide. Can you guide me a bit
> more towards a good approach?
You're hitting a property called type invariance. See
http://docs.julialang.org/en/release-0.4/manual/types/#parametric-compo
site-types
There's nothing wrong with writing foo{T<:Number}(a::Vector{T}).
That's the recommended way, though that it's a bit verbose (maybe a
shorter syntax will be added at some point).
Regards
> Thanks
>
> On Wed, Jan 6, 2016 at 1:27 PM, James Gilbert <[email protected]>
> wrote:
> > You'd think, reading this forum, that the preferred style is to
> > specify the type of function arguments. I think that's what feels
> > right for people with experience in other languages. Specifying
> > argument types doesn't necessarily improve speed, and harms the
> > reusability of code.
> >
