add opt in support for non trivial inner constuctors (JuliaArrays#17)

* remove createinstance

* Make skipping constructor opt in

Author: Pietro Vertechi

src/utils.jl

@@ -5,6 +5,8 @@ eltypes(::Type{T}) where {T<:Tuple} =
     tuple_type_cons(eltype(tuple_type_head(T)), eltypes(tuple_type_tail(T)))
 eltypes(::Type{NamedTuple{K, V}}) where {K, V} = eltypes(V)
 
+Base.@pure SkipConstructor(::Type) = false
+
 @generated function get_ith(s::StructArray{T}, I...) where {T}
     args = []
     for key in fields(T)
@@ -31,8 +33,18 @@ end
     end
 end
 
-createinstance(::Type{T}, args...) where {T} = T(args...)
+function createinstance(::Type{T}, args...) where {T}
+    SkipConstructor(T) ? unsafe_createinstance(T, args...) : T(args...)
+end
+
 createinstance(::Type{T}, args...) where {T<:Union{Tuple, NamedTuple}} = T(args)
 
+@generated function unsafe_createinstance(::Type{T}, args...) where {T}
+    v = fieldnames(T)
+    new_tup = Expr(:(=), Expr(:tuple, v...), :args)
+    construct = Expr(:new, :T, (:(convert(fieldtype(T, $(Expr(:quote, sym))), $sym)) for sym in v)...)
+    Expr(:block, new_tup, construct)
+end
+
 createtype(::Type{T}, ::Type{C}) where {T<:NamedTuple{N}, C} where {N} = NamedTuple{N, C}
 createtype(::Type{T}, ::Type{C}) where {T, C} = T

test/runtests.jl

@@ -116,4 +116,17 @@ end
     @test Tables.rowaccess(s)
     @test Tables.columnaccess(s)
 end
-    
+
+struct S
+    x::Int
+    y::Float64
+    S(x) = new(x, x)
+end
+
+StructArrays.SkipConstructor(::Type{<:S}) = true
+
+@testset "inner" begin
+    v = StructArray{S}([1], [1])
+    @test v[1] == S(1)
+    @test v[1].y isa Float64
+end