On Wednesday, November 5, 2014 5:43:39 AM UTC+11, Evan Pu wrote:
>
> It does indeed happens inside the function, if you pass a function as an
> argument to it (rather than refering to f implicitly in the function body,
> you explicitly pass in f as an extra argument)
> see below:
>
> julia> f(x) = x + 1
> f (generic function with 1 method)
>
> julia> g(f, xs) = [f(x) for x in xs]
> g (generic function with 1 method)
>
When this is being compiled Julia has no way of knowing what type f()
returns since its a runtime parameter, so it has to use Any.
>
> julia> xs = [1,2,3]
> 3-element Array{Int64,1}:
> 1
> 2
> 3
>
> julia> g(f,xs)
> 3-element Array{Any,1}:
> 2
> 3
> 4
>
>
> On Tuesday, November 4, 2014 2:22:24 AM UTC-5, Jutho wrote:
>>
>> This only happens in global scope, not inside a function? If you define
>> f(list) = return [g(x) for x in list]
>>
>> then f(xs) will return an Array{Float64,1}.
>>
>> Op dinsdag 4 november 2014 03:23:36 UTC+1 schreef K leo:
>>>
>>> I found that I often have to force this conversion, which is not too
>>> difficult. The question why comprehension has to build with type Any?
>>>
>>>
>>> On 2014年11月04日 07:06, Miguel Bazdresch wrote:
>>> > > How could I force the type of gxs1 to be of an array of Float64?
>>> >
>>> > The simplest way is:
>>> >
>>> > gxs1 = Float64[g(x) for x in xs]
>>> >
>>> > -- mb
>>> >
>>> > On Mon, Nov 3, 2014 at 6:01 PM, Evan Pu <[email protected]
>>> > <mailto:[email protected]>> wrote:
>>> >
>>> > Consider the following interaction:
>>> >
>>> > julia> g(x) = 1 / (1 + x)
>>> > g (generic function with 1 method)
>>> >
>>> > julia> typeof(g(1.0))
>>> > Float64
>>> >
>>> > julia> xs = [1.0, 2.0, 3.0, 4.0]
>>> > 4-element Array{Float64,1}:
>>> > 1.0
>>> > 2.0
>>> > 3.0
>>> > 4.0
>>> >
>>> > julia> gxs1 = [g(x) for x in xs]
>>> > 4-element Array{Any,1}:
>>> > 0.5
>>> > 0.333333
>>> > 0.25
>>> > 0.2
>>> >
>>> > Why isn't gxs1 type of Array{Float64,1}?
>>> > How could I force the type of gxs1 to be of an array of Float64?
>>> >
>>> > julia> gxs2 = [convert(Float64,g(x)) for x in xs]
>>> > 4-element Array{Any,1}:
>>> > 0.5
>>> > 0.333333
>>> > 0.25
>>> > 0.2
>>> >
>>> > somehow this doesn't seem to work...
>>> >
>>> >
>>> >
>>> >
>>>
>>>
