What's the motivation for wanting to restrict calling repack on
non-composite types? 'fieldnames' works fine on them too.
If you want to do a different operation on non-composites, wouldn't you
have to define specialized methods for different type families anyway since
they would all have different interfaces/behaviors?
On Friday, May 1, 2015 at 10:12:15 AM UTC-4, Tamas Papp wrote:
> The use case is the following: I have parameters to various economic
> models in composite (immutable) types. Each model maps to a set of
> moments, for which I have data, and I am calling NLopt to find the
> parameters for which the moments match the data. For this, I need to be
> able to convert back and forth between immutable types and vectors
> (which can be passed to NLopt).
>
> I am using the function
>
> repack(schema, value, outputtype)
>
> The same value may be mapped in multiple ways, hence `schema`. For
> example, a schema could be that various fields of a composite type are
> ignored or constrained.
>
> A straightforward natural mapping when the schema is the composite type
> itself is
>
> repack(T::DataType, x::T, ::Type{Vector}) = [getfield(x,f) for f =
> fieldnames(x)]
>
> I want to write a short version
>
> repack{T}(x::T, outputtype) = repack(T, x, outputtype)
>
> that only gets called when T is a DataType. I don't know how to do this.
>
> But in the meantime I realized that DataType is not what I want anyway,
> I want to test for composite types, but that has no explicit type.
>
> Best,
>
> Tamas
>
>
> On Fri, May 01 2015, Tom Breloff <[email protected] <javascript:>> wrote:
>
> > If I understand correctly, you want to pass an instance of Foo into
> fun2,
> > which would then effectively call "fun1(Foo, Foo())". I don't quite
> > understand the use case... can you give an example of when the second
> > "fun1" definition would be called?
> >
> > On Friday, May 1, 2015 at 9:24:59 AM UTC-4, Tamas Papp wrote:
> >>
> >> Not really --- I wanted to dispatch on something being an _instance_ of
> >> a type that is a DataType. Having reread the manual, I don't think that
> >> is possible directly, but works with one level of indirection:
> >>
> >> fun1(T::DataType,x) = "do something with $x"
> >> fun1(T, x) = "this is not a datatype"
> >> fun2{T}(x::T) = fun1(T,x)
> >> type Foo end
> >> fun2(Foo())
> >>
> >> That said, I realized that DataType is not what I need.
> >>
> >> Best,
> >>
> >> Tamas
> >>
> >> On Thu, Apr 30 2015, Tom Breloff <[email protected] <javascript:>>
> wrote:
> >>
> >> > Is this what you're looking for?
> >> >
> >> >
> >> > julia> yyy(x::DataType) = true
> >> > yyy (generic function with 1 method)
> >> >
> >> >
> >> > julia> yyy(x) = false
> >> > yyy (generic function with 2 methods)
> >> >
> >> >
> >> > julia> yyy(Int)
> >> > true
> >> >
> >> >
> >> > julia> yyy(5)
> >> > false
> >> >
> >> >
> >> >
> >> >
> >> > On Thursday, April 30, 2015 at 11:04:02 AM UTC-4, Tamas Papp wrote:
> >> >>
> >> >> This is toy problem that came up in the context of something larger,
> >> >> reduced to be simple so that I can ask about it more easily.
> >> >>
> >> >> Suppose I want to implement the function
> >> >>
> >> >> is_instanceof_datatype(x) = is(typeof(x),DataType)
> >> >>
> >> >> using dispatch: a default method that is
> >> >>
> >> >> is_instanceof_datatype(x) = false
> >> >>
> >> >> and some other method which only gets called when x is an instance
> of a
> >> >> DataType:
> >> >>
> >> >> is_instanceof_datatype{ ... }(x::T) = true # how to dispatch
> >> >>
> >> >> but I don't know how to do the latter, hence the ....
> >> >>
> >> >> The context is that I want to write a method that, for instances of
> >> >> DataTypes, returns the slots in a given order, but for other values
> it
> >> >> does something else, and I don't know how to do this.
> >> >>
> >> >> Best,
> >> >>
> >> >> Tamas
> >> >>
> >>
>
