add separate instance based similar

Author: Pietro Vertechi

src/structarray.jl

@@ -69,9 +69,12 @@ function Base.similar(::Type{StructArray{T, N, C}}, sz::Dims) where {T, N, C}
     StructArray{T}(cols)
 end
 
-Base.similar(s::S, sz::Tuple) where {S<:StructArray} = similar(S, Base.to_shape(sz))
-Base.similar(s::S, sz::Base.DimOrInd...) where {S<:StructArray} = similar(S, Base.to_shape(sz))
-Base.similar(s::S) where {S<:StructArray} = similar(S, Base.to_shape(axes(s)))
+Base.similar(s::StructArray, sz::Tuple) = similar(s, Base.to_shape(sz))
+Base.similar(s::StructArray, sz::Base.DimOrInd...) = similar(s, Base.to_shape(sz))
+Base.similar(s::StructArray) = similar(s, Base.to_shape(axes(s)))
+function Base.similar(s::StructArray{T}, sz::Dims) where {T}
+    StructArray{T}(map(typ -> similar(typ, sz), fieldarrays(s)))
+end
 
 fieldarrays(s::StructArray) = getfield(s, :fieldarrays)