On Sun, Oct 11, 2015 at 6:54 PM, Andrei Zh <[email protected]> wrote:
> I didn't know about such capability, thanks. But I still can't figure out
> how to call this constructor. E.g.:
>
> julia> Bar{Int}()
> ERROR: MethodError: `convert` has no method matching
> convert(::Type{Bar{Int64}})
> This may have arisen from a call to the constructor Bar{Int64}(...),
> since type constructors fall back to convert methods.
> Closest candidates are:
> convert{T}(::Type{T}, !Matched::T)
> Bar{#s6,T}()
> call{T}(::Type{T}, !Matched::Any)
> in call at essentials.jl:57
>
> Don't know if it matters, but I also have a different output of
> `methods(Bar{Int})` than you:
>
> julia> methods(Bar{Int})
> 3-element Array{Any,1}:
> call{#s6,T}(::Type{Bar{#s6}}) at
> /home/<username>/work/playground/contructors.jl:11
> call{T}(::Type{T}, arg) at essentials.jl:56
> call{T}(::Type{T}, args...) at essentials.jl:57
>
The error I get (which seems to be different from yours) is
```
julia> type Bar{T}
x::Array{T,1}
Bar() = Bar(zeros(T, 10))
end
julia> Bar{Int}()
ERROR: MethodError: `convert` has no method matching
convert(::Type{Bar{T}}, ::Array{Int64,1})
This may have arisen from a call to the constructor Bar{T}(...),
since type constructors fall back to convert methods.
Closest candidates are:
call{T}(::Type{T}, ::Any)
convert{T}(::Type{T}, ::T)
in call at ./none:3
```
And the issue here is that you cannot call the non-existing default
inner constructor if you provide your own one. I suspect `Foo()` won't
work for you either.
The following works for me
```
julia> type Bar{T}
x::Array{T,1}
Bar() = new(zeros(T, 10))
end
julia> Bar{Int}()
Bar{Int64}([0,0,0,0,0,0,0,0,0,0])
```
>
>
>
>
> On Monday, October 12, 2015 at 1:06:14 AM UTC+3, Yichao Yu wrote:
>>
>> On Sun, Oct 11, 2015 at 5:57 PM, Andrei Zh <[email protected]> wrote:
>> > Let's consider 2 types with inner constructors:
>> >
>> > type Foo
>> > x::Array{Int,1}
>> >
>> >
>> > Foo() = Foo(zeros(Int, 10))
>> > end
>> >
>> > type Bar{T}
>> > x::Array{T,1}
>> >
>> >
>> > Bar() = Bar(zeros(T, 10))
>> > end
>> >
>> > The only difference between them is that `Bar` has type parameter while
>> > `Foo` doesn't. I'd expect their inner constructors behave the same way,
>> > but
>> > `Bar` turns to ignore inner constructor definition:
>> >
>> > julia> methods(Foo)
>> > 3-element Array{Any,1}:
>> > call(::Type{Foo}) at /home/<username>/work/playground/contructors.jl:5
>> > call{T}(::Type{T}, arg) at essentials.jl:56
>> > call{T}(::Type{T}, args...) at essentials.jl:57
>> >
>> >
>> > julia> methods(Bar)
>> > 2-element Array{Any,1}:
>> > call{T}(::Type{T}, arg) at essentials.jl:56
>> > call{T}(::Type{T}, args...) at essentials.jl:57
>> >
>> > Is it a bug or a feature and how to make `Bar` recognize inner
>> > constructor
>> > (outer constructor is not an option here since it uses type parameter
>> > `T` in
>> > constructor body, but not in its constructor)?
>> >
>>
>> As you pointed out, the inner constructor can access the type
>> parameter and therefore the type parameter needs to be specified in
>> order to call it.
>>
>> julia> methods(Bar{Int})
>> 3-element Array{Any,1}:
>> call{T}(::Type{Bar{T}}) at none:3
>> call{T}(::Type{T}, arg) at essentials.jl:55
>> call{T}(::Type{T}, args...) at essentials.jl:56
