Fix handling of object references

Turns out I never implemented the reading part of this

src/JLD.jl

@@ -295,7 +295,6 @@ function read(parent::Union(JldFile, JldGroup), name::ByteString)
 end
 read(parent::Union(JldFile,JldGroup), name::Symbol) = read(parent,bytestring(string(name)))
 
-# read and readsafely differ only in how they handle CompositeKind
 function read(obj::JldDataset)
     dtype = datatype(obj.plain)
     dspace_id = HDF5.h5d_get_space(obj.plain)
@@ -410,12 +409,17 @@ end
 
 # Read a reference
 function read_ref(f::JldFile, ref::HDF5ReferenceObj)
+    haskey(f.jlref, ref) && return f.jlref[ref].value
+
     dset = f[ref]
-    try
-        return read(dset)
+    data = try
+        read(dset)
     finally
         close(dset)
     end
+
+    f.jlref[ref] = WeakRef(data)
+    data
 end
 function getrefs{T}(obj::JldDataset, ::Type{T})
     refs = read(obj.plain, Array{HDF5ReferenceObj})

test/jld.jl

@@ -123,6 +123,19 @@ immutable MyImmutable2
     MyImmutable2() = new()
 end
 nonpointerfree_immutable_3 = MyImmutable2()
+# Array references
+arr_contained = [1, 2, 3]
+arr_ref = typeof(arr_contained)[]
+push!(arr_ref, arr_contained, arr_contained)
+# Object references
+type ObjRefType
+    x::ObjRefType
+    y::ObjRefType
+    ObjRefType() = new()
+    ObjRefType(x, y) = new(x, y)
+end
+ref1 = ObjRefType()
+obj_ref = ObjRefType(ObjRefType(ref1, ref1), ObjRefType(ref1, ref1))
 
 iseq(x,y) = isequal(x,y)
 iseq(x::MyStruct, y::MyStruct) = (x.len == y.len && x.data == y.data)
@@ -247,6 +260,8 @@ end
 @write fid nonpointerfree_immutable_1
 @write fid nonpointerfree_immutable_2
 @write fid nonpointerfree_immutable_3
+@write fid arr_ref
+@write fid obj_ref
 # Make sure we can create groups (i.e., use HDF5 features)
 g = g_create(fid, "mygroup")
 i = 7
@@ -331,6 +346,12 @@ for mmap = (true, false)
     @check fidr nonpointerfree_immutable_1
     @check fidr nonpointerfree_immutable_2
     @check fidr nonpointerfree_immutable_3
+    arr = read(fidr, "arr_ref")
+    @test arr == arr_ref
+    @test arr[1] === arr[2]
+    obj = read(fidr, "obj_ref")
+    @test obj.x.x === obj.x.y == obj.y.x === obj.y.y
+    @test obj.x !== obj.y
 
     x1 = read(fidr, "group1/x")
     @assert x1 == {1}