Add isopen(obj::HDF5File) (#399)

* Add isopen(obj::HDF5File)

src/HDF5.jl

@@ -8,7 +8,7 @@ using Compat: unsafe_convert, String
 import Base: 
     ==, close, convert, done, dump, eltype, endof, flush, getindex,
     isempty, isvalid, length, names, ndims, next, parent, read,
-    setindex!, show, size, sizeof, start, write
+    setindex!, show, size, sizeof, start, write, isopen
 
 export
     # types
@@ -690,6 +690,13 @@ function close(obj::HDF5File)
     nothing
 end
 
+"""
+    isopen(obj::HDF5File)
+
+Returns `true` if `obj` has not been closed, `false` if it has been closed.
+"""
+isopen(obj::HDF5File) = obj.id != -1
+
 for (h5type, h5func) in
     ((:(Union{HDF5Group, HDF5Dataset}), :h5o_close),
      (:HDF5Attribute, :h5a_close))

test/plain.jl

@@ -10,6 +10,7 @@ using Compat.String
     # Create a new file
     fn = joinpath(tempdir(),"test.h5")
     f = h5open(fn, "w")
+    @test isopen(f)
     # Write scalars
     f["Float64"] = 3.2
     f["Int16"] = Int16(4)
@@ -107,6 +108,7 @@ using Compat.String
     # Create a dataset designed to be deleted
     f["deleteme"] = 17.2
     close(f)
+    @test !isopen(f)
     # Test the h5read/write interface, with attributes
     W = copy(reshape(1:120, 15, 8))
     Wa = Dict("a"=>1, "b"=>2)