use only type in traits

Author: jishnub

base/range.jl

@@ -859,9 +859,8 @@ copy(r::AbstractRange) = r
 # This is especially important for wrapper types, as they may choose the
 # use the parent's iterate method instead of the fallback implementation by defining
 # their IterationStyle to be the same as their parents'.
-struct IterationStyle{T}
-    x :: T
-end
+struct IterationStyle{T} end
+IterationStyle(x) = IterationStyle{typeof(x)}()
 
 iterate(r::Union{StepRangeLen, LinRange}, i::Integer = zero(length(r))) = _iterate(r, IterationStyle(r), i)
 function _iterate(r::AbstractArray, ::IterationStyle{<:AbstractRange}, i = zero(length(r)))