All true.
One tip: if you want to find out what abstract type is a parent to all the
concrete types you're interested in, you can use the "typejoin" function.
julia> typejoin(Array, LinSpace)
AbstractArray{T,N}
julia> typejoin(Vector,LinSpace)
AbstractArray{T,1}
On Wednesday, October 21, 2015 at 12:05:06 PM UTC-4, Steven G. Johnson
wrote:
>
>
>
> On Wednesday, October 21, 2015 at 11:57:08 AM UTC-4, Jonathan Malmaud
> wrote:
>>
>> Just to add to Spencer's answer: Is there a particular reason to have
>> your function arguments have type annotations at all in the function
>> definition? You could just write
>>
>> function f(x)
>> y= x[3:5] # or whatever
>> z = length(x)
>> end
>>
>> and now someone could call f with any kind of object that supports
>> indexing and "length" and it will work. This is "duck-typing", if you're
>> familiar with that term, and is the dominant paradigm in Julia precisely
>> since it makes generic programming easier.
>>
>>>
> I agree that duck typing is often a good practice, but there are three
> good reasons to declare argument types:
>
> * Correctness: the code might work but give unexpected results if you pass
> the wrong types. e.g. fib(n) = n < 2 ? one(n) : fib(n-1)+fib(n-2) is a
> function that computes the Fibonacci numbers only for integers — it gives
> an answer for floating-point n, but the answer is probably not what you
> want.
>
> * Clarity: sometimes it is a useful hint to the caller if you indicate the
> expected type.
>
> * Dispatch: you want to do different things for different types, so you
> use the argument types as a filter to indicate which methods should work
> when.
>
> However, in all cases the trick is to declare the widest applicable
> argument type. e.g. use fib(n::Integer), not fib(n::Int), so that any
> integer type will be accepted, rather than the concrete type Int.
>
> In the case of functions accepting vectors, you should almost always
> declare the type as AbstractVector or AbstractArray, not Vector or Array.
> That will let you handle any array-like type. In particular, ranges are a
> subtype of AbstractVector.
>
