bypass constructor on getindex (#145)

* bypass constructor in getindex

* special case tuples and named tuples

* only bypass constructor for concrete types

* test on internal constructor case

* minor reorg

* define struct outside testet

Author: Pietro Vertechi

src/interface.jl

@@ -9,5 +9,8 @@ end
 
 staticschema(::Type{T}) where {T<:Tup} = T
 
-createinstance(::Type{T}, args...) where {T} = T(args...)
-createinstance(::Type{T}, args...) where {T<:Union{Tuple, NamedTuple}} = T(args)
+function createinstance(::Type{T}, args...) where {T}
+    isconcretetype(T) ? bypass_constructor(T, args) : T(args...)
+end
+
+createinstance(::Type{T}, args...) where {T<:Tup} = T(args)

src/utils.jl

@@ -146,3 +146,16 @@ hasfields(::Type{<:NTuple{N, Any}}) where {N} = true
 hasfields(::Type{<:NamedTuple{names}}) where {names} = true
 hasfields(::Type{T}) where {T} = !isabstracttype(T)
 hasfields(::Union) = false
+
+"""
+    bypass_constructor(T, args)
+
+Create an instance of type `T` from a tuple of field values `args`, bypassing
+possible internal constructors. `T` should be a concrete type.
+"""
+@generated function bypass_constructor(::Type{T}, args) where {T}
+    vars = ntuple(_ -> gensym(), fieldcount(T))
+    assign = [:($var::$(fieldtype(T, i)) = getfield(args, $i)) for (i, var) in enumerate(vars)]
+    construct = Expr(:new, :T, vars...)
+    Expr(:block, assign..., construct)
+end

test/runtests.jl

@@ -238,6 +238,20 @@ end
     @test getproperty(t, 2) == [3.0, 2.0]
 end
 
+struct A
+    x::Int
+    y::Int
+    A(x) = new(x, x)
+end
+
+@testset "internal constructor" begin
+    v = A.([1, 2, 3])
+    s = StructArray(v)
+    @test s[1] == A(1)
+    @test s[2] == A(2)
+    @test s[3] == A(3)
+end
+
 @testset "kwargs constructor" begin
     a = [1.2]
     b = [2.3]