On Wednesday, October 28, 2015 at 8:10:41 AM UTC-4, Stefan Karpinski wrote:
>
> The key behavioral difference between these two is that with the
> non-parametric union version you can change both the value and the type of
> the field of a MyType object after construction, whereas in the parametric
> version you can change the value of the field after an object has been
> constructed, but not the type – since the object is either a MyType{Int} or
> a MyType{Float64}.
>
Given that reasoning, is there any reason to have an immutable with fields
that have abstract/unspecified types? Isn't it always better to use a
parametric type?
>
> On Wed, Oct 28, 2015 at 3:21 AM, Gnimuc Key <gnim...@gmail.com
> <javascript:>> wrote:
>
>> that makes sense. many thanks!
>>
>> 在 2015年10月28日星期三 UTC+8下午3:14:26，Tomas Lycken写道：
>>
>>> With a type declared like that, any access of the field x will be type
>>> unstable, which means that Julia’s JIT compiler will emit much more
>>> defensive, and thus slower, code.
>>>
>>> The solution is to declare a *parametric* type:
>>>
>>> type MyType{T<:Union{Int64, Float64}}
>>> x::T
>>> end
>>>
>>> That way, MyType(3) and MyType(3.0) will now be instances of different
>>> types, and the compiler can generate fast code. (You can still write
>>> functions that dispatch on just MyType, so you don’t loose any
>>> expressive power…)
>>>
>>> // T
>>>
>>> On Wednesday, October 28, 2015 at 5:10:09 AM UTC+1, Gnimuc Key wrote:
>>>
>>> Avoid type Unions in fields ¶
>>>>>
>>>>> <http://docs.julialang.org/en/latest/manual/style-guide/#avoid-strange-type-unions>
>>>>> type MyType
>>>>> ...
>>>>> x::Union{Void,T}
>>>>> end
>>>>
>>>>
>>>> I'm wondering whether it's a good style or not to write something like
>>>> this:
>>>>
>>>> type MyType
>>>> ...
>>>> x::Union{Int64,Float64}end
>>>>
>>>> what's the side effects of using Union like this?
>>>>
>>>
>>>
>>
>
