Fix references to immutables

Resolves #53 using the changes suggested by Jameson Nash @vtjnash.
However, we don't wan't to actually call these functions for speed
(for that we want to use `ccall` and `&`) but it does aid in
compatibility.

Author: Andy Ferris

src/FieldVector.jl

@@ -27,6 +27,9 @@ abstract FieldVector{T} <: StaticVector{T}
 @inline getindex(v::FieldVector, i::Integer) = getfield(v, i)
 @inline setindex!(v::FieldVector, x, i::Integer) = setfield!(v, i, x)
 
-@inline function Base.unsafe_convert{T}(::Type{Ptr{T}}, v::FieldVector{T})
-    Base.unsafe_convert(Ptr{T}, Base.data_pointer_from_objref(v))
-end
+# See #53
+Base.cconvert{T}(::Type{Ptr{T}}, v::FieldVector) = Ref(v)
+Base.unsafe_convert{T, FV <: FieldVector}(::Type{Ptr{T}}, m::Ref{FV}) =
+    _unsafe_convert(Ptr{T}, eltype(FV), m)
+_unsafe_convert{T, FV <: FieldVector}(::Type{Ptr{T}}, ::Type{T}, m::Ref{FV}) =
+         Ptr{T}(Base.unsafe_convert(Ptr{FV}, m))

src/SArray.jl

@@ -64,7 +64,6 @@ end
 
 @inline SArray(a::StaticArray) = SArray{size(typeof(a))}(Tuple(a))
 
-
 # Some more advanced constructor-like functions
 @inline eye{Size}(::Type{SArray{Size}}) = eye(SArray{Size,Float64})
 @inline zeros{Size}(::Type{SArray{Size}}) = zeros(SArray{Size,Float64})
@@ -87,9 +86,10 @@ end
 
 @inline Tuple(v::SArray) = v.data
 
-@inline function Base.unsafe_convert{Size,T}(::Type{Ptr{T}}, a::SArray{Size,T})
-    Base.unsafe_convert(Ptr{T}, Base.data_pointer_from_objref(a))
-end
+# See #53
+Base.cconvert{T}(::Type{Ptr{T}}, a::SArray) = Ref(a)
+Base.unsafe_convert{S,T,D,L}(::Type{Ptr{T}}, a::Ref{SArray{S,T,D,L}}) =
+    Ptr{T}(Base.unsafe_convert(Ptr{SArray{S,T,D,L}}, a))
 
 macro SArray(ex)
     if !isa(ex, Expr)

src/SMatrix.jl

@@ -118,9 +118,10 @@ end
 
 @inline Tuple(v::SMatrix) = v.data
 
-@inline function Base.unsafe_convert{N,M,T}(::Type{Ptr{T}}, m::SMatrix{N,M,T})
-    Base.unsafe_convert(Ptr{T}, Base.data_pointer_from_objref(m))
-end
+# See #53
+Base.cconvert{T}(::Type{Ptr{T}}, m::SMatrix) = Ref(m)
+Base.unsafe_convert{N,M,T,L}(::Type{Ptr{T}}, m::Ref{SMatrix{N,M,T,L}}) =
+    Ptr{T}(Base.unsafe_convert(Ptr{SMatrix{N,M,T,L}}, m))
 
 
 macro SMatrix(ex)

src/SVector.jl

@@ -49,9 +49,10 @@ end
 
 @inline Tuple(v::SVector) = v.data
 
-@inline function Base.unsafe_convert{N,T}(::Type{Ptr{T}}, v::SVector{N,T})
-    Base.unsafe_convert(Ptr{T}, Base.data_pointer_from_objref(v))
-end
+# See #53
+Base.cconvert{T}(::Type{Ptr{T}}, v::SVector) = Ref(v)
+Base.unsafe_convert{N,T}(::Type{Ptr{T}}, v::Ref{SVector{N,T}}) =
+    Ptr{T}(Base.unsafe_convert(Ptr{SVector{N,T}}, v))
 
 # Converting a CartesianIndex to an SVector
 convert(::Type{SVector}, I::CartesianIndex) = SVector(I.I)