On Thu, 2016-09-15 at 01:19, Jeffrey Sarnoff wrote:
> Thanks for updating your work.
> If there is a form that allows a function to be defined that has
> multidispatch over trait and also over type, please provide an example.
> (If it is already there, please direct me to that example).
Yep, that was missing in the docs, thanks! I added a section with
example here:
https://github.com/mauro3/SimpleTraits.jl#details-of-method-dispatch
Basically, dispatch first happens on the types as usual. If the method
thus selected is a trait-method then trait dispatch kicks in. This is
how it naturally happens with Tim's trick but also how it makes most
sense (to me).
> On Wednesday, September 14, 2016 at 6:04:04 AM UTC-4, Mauro wrote:
>>
>> There is --at times-- some interest on this list about traits, enough
>> that I thought the noise to announce the registration of this traits
>> package is warranted. In brief, traits group types into sets
>> independent of the type hierarchy and let functions dispatch on those
>> traits instead of on types.
>>
>> The package can be found here:
>> https://github.com/mauro3/SimpleTraits.jl
>>
>> SimpleTraits.jl provides macros to automate *Tim's trait trick*. A
>> brief example (more can be found in the README):
>>
>> using SimpleTraits
>> # define a trait:
>> @traitdef IsNice{X}
>>
>> # add some types to the trait:
>> @traitimpl IsNice{Int}
>> @traitimpl IsNice{String}
>>
>> # define a function dispatching on this trait and its negation:
>> @traitfn f{X; IsNice{X}}(x::X) = "Very nice!"
>> @traitfn f{X; !IsNice{X}}(x::X) = "Not so nice!"
>>
>> # use that function like any other function
>> f(5) # => "Very nice!"
>> f("a") # => "Very nice!"
>> f(6.0) # => "Not so nice!"
>>
>>
>> Tim Holy, indeed the inventor of the trick named after him, uses
>> SimpleTraits in the overhaul of his Images.jl package [1,2] (and was who
>> prodded me to register SimpleTraits.jl). The "blurb" in my README is:
>>
>> Tim Holy endorses SimpleTraits, a bit: "I'd say that compared to
>> manually writing out the trait-dispatch, the "win" is not enormous,
>> but it is a little nicer." I suspect that — if you don't write
>> Holy-traits before breakfast — your "win" should be greater ;-)
>>
>> [1] https://github.com/timholy/Images.jl/issues/542
>> [2] https://github.com/JuliaImages/ImageAxes.jl
>>
