Combining SimpleTraits.jl traits on one type

General Usage
2

From the README on SimpleTraits.jl it appears dispatching on multiple traits is not yet possible.

However WhereTraits.jl could possibly support it!

using WhereTraits

abstract type AbstractA end
abstract type DecoA <: AbstractA end

# A few concrete types
struct A <: AbstractA end
struct A1 <: DecoA end
struct A2 <: DecoA end
struct A3 <: DecoA end

# just some function
f(::AbstractA, x) = x+2
g(::DecoA, x, y) = x+y

is_nice(::Type{<:A1}) = true
is_nice(::Type{<:DecoA}) = false

is_cool(::Type{<:A2}) = true
is_cool(::Type{<:DecoA}) = false

@traits f(a::TA, x) where {TA <: DecoA, is_nice(TA)} = g(a,x,3)
@traits f(a::TA, x) where {TA <: DecoA, is_cool(TA)} = g(a,x,5)
@traits f(a::TA, x) where {TA <: DecoA, !is_cool(TA), !is_nice(TA)} = "without this the multiple dispatch is ill-defined for `A3`"

@show f(A(),0)
@show f(A1(),0)
@show f(A2(),0)
@show f(A3(),0)
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