Annoyingly this inverts the behavior, so I have to provide both inner and
outer constructors for this and the obvious outer constructor may not be
defined as it calls itself. (There is a solution below. )
Additionally it seems confusing that the new() method in in the constructor
does not call the zero parameter constructor, e.g. there is not constructor
chaining
If you run this example you get an undefined value of t in Foo and the
un-typed version does not work
abstract Bar
type Foo{T} <: Bar
t::T
Foo() = new( zero( T ) )
Foo( d::T) = ( this = new() ; this )
end
Foo{Int}( 1)
Foo( 1)
The below works but is not obvious - without the Foo{T} loops into
eternity. Note the duplication of code between the one arg constructor and
the two arg.
abstract Bar
type Foo{T} <: Bar
t::T
Foo() = new( zero( T ) )
Foo( d::T) = ( this = new( zero( T ) ; this )
end
*Foo{T}(d::T) = Foo{T}( d )*
On Tuesday, February 10, 2015 at 12:47:19 PM UTC-5, Stefan Karpinski wrote:
>
> Supplying the type parameter explicitly invokes the inner constructor. For
> non-parametric types, there's a single generic function that both inner and
> outer constructor methods belong to – so the only distinction between the
> inner and outer ones is where they occur (and thus whether they have access
> to new or not). For parametric types, however, inner constructor methods
> are added to the Foo{T} object whereas outer constructor methods are added
> to the Foo object. It's a but confusing, I know.
>
> On Tue, Feb 10, 2015 at 12:38 PM, Michael Francis <[email protected]
> <javascript:>> wrote:
>
>> But why is the outer constructor not called in this case ?
>>
>> On Tuesday, February 10, 2015 at 12:35:44 PM UTC-5, Stefan Karpinski
>> wrote:
>>>
>>> The inner constructor only has a zero-argument method:
>>>
>>> julia> Foo{Int}()
>>> Foo{Int64}(0)
>>>
>>>
>>> If you add a second inner constructor method, then you can call it.
>>>
>>> On Tue, Feb 10, 2015 at 12:15 PM, Michael Francis <[email protected]>
>>> wrote:
>>>
>>>> A slightly simplified example, If I pin the type parameter I am unable
>>>> to create the new object. I'm sure I'm missing something obvious here but
>>>> given that Int 1 defaults to Int64 on my system I would expect both lines
>>>> to work ?
>>>>
>>>> abstract Bar
>>>> type Foo{T} <: Bar
>>>> t::T
>>>> Foo() = new( zero( T ) )
>>>> end
>>>> Foo{T}( d::T) = ( this = Foo{T}() ; this.t = d; this )
>>>>
>>>> Foo{Int}( 1) # Foo{Int64} has no method matching Foo{Int64}(::Int64)
>>>> Foo( 1) # Works
>>>>
>>>
>>>
>
