[julia-users] Type stability of function in composite types

[Giuseppe Ragusa]

I am failing to understand why the following code produce type instability 
(caveat: the code is a reduction o large and more complex code, but the 
features are the same). 

```
type Foo
  f::Function
  y::Array{Float64, 1}
  x::Array{Float64, 2}  
end

type Bar{T}
  b::T
end

type A{T}
  a::T
end

x = randn(100,4)
y = randn(100)

f(theta, y, x) = x'*(y-x*theta)

(g::Foo)(x) = g.f(x, g.y, g.x)

a = A(Bar(Foo(f, y, x)))

m(a::A) = a.a.b([.1,.1,.1,.1])
```

The output of @code_warntype is below:

```
@code_warntype m(a)

Variables:
  #self#::#m
  a::A{Bar{Foo}}

Body:
  begin
      SSAValue(1) = 
(Core.getfield)((Core.getfield)(a::A{Bar{Foo}},:a)::Bar{Foo},:b)::Foo
      SSAValue(0) = $(Expr(:invoke, LambdaInfo for vect(::Float64, 
::Vararg{Float64,N}), :(Base.vect), 0.1, 0.1, 0.1, 0.1))
      return 
((Core.getfield)(SSAValue(1),:f)::F)(SSAValue(0),(Core.getfield)(SSAValue(1),:y)::Array{Float64,1},(Core.getfield)(SSAValue(1),:x)::Array{Float64,2})::Any
  end::Any
```

I thought the v0.5 will solve the problem with functions not being 
correctly inferred. Maybe, I am simply doing something patently stupid.