ndarray: implement size(x, dims...) (#350)

```julia
julia> x = mx.NDArray([1 2; 3 4; 5 6])
3×2 mx.NDArray{Int64,2} @ CPU0:
 1  2
 3  4
 5  6

julia> size(x, 1, 2, 3, 4)
(3, 2, 1, 1)
```

NEWS.md

@@ -16,6 +16,22 @@
   (MXNet.mx.SymbolicNode x, MXNet.mx.SymbolicNode y, MXNet.mx.SymbolicNode z)
   ```
 
+### `NDArray`
+
+* `size(x, dims...)` is supported now. (#TBD)
+
+  ```julia
+  julia> x = mx.NDArray([1 2; 3 4; 5 6])
+  3×2 mx.NDArray{Int64,2} @ CPU0:
+   1  2
+   3  4
+   5  6
+
+  julia> size(x, 1, 2, 3, 4)
+  (3, 2, 1, 1)
+
+  ```
+
 # v0.3.0 (2017.11.16)
 
 * Update `libmxnet` to

src/ndarray.jl

@@ -226,22 +226,29 @@ import Base: size, length, ndims, eltype
 
 """
     size(x::NDArray)
-    size(x::NDArray, dim)
+    size(x::NDArray, dims...)
 
 Get the shape of an `NDArray`. The shape is in Julia's column-major convention.
 See also the notes on NDArray shapes [`NDArray`](@ref).
 """
-function size(arr :: NDArray)
+function size(x::NDArray)
   ref_ndim  = Ref{MX_uint}(0)
   ref_shape = Ref{Ptr{MX_uint}}(0)
   @mxcall(:MXNDArrayGetShape, (MX_handle, Ref{MX_uint}, Ref{Ptr{MX_uint}}),
-          arr, ref_ndim, ref_shape)
+          x, ref_ndim, ref_shape)
   tuple(map(Int, flipdim(unsafe_wrap(Array, ref_shape[], ref_ndim[]),1))...)
 end
-function size(arr :: NDArray, dim :: Int)
-  size(arr)[dim]
+
+function size(x::NDArray{T,N}, dim::Int) where {T,N}
+  if dim > N
+    1
+  else
+    size(x)[dim]
+  end
 end
 
+size(x::NDArray, dims::Int...) = map(d -> size(x, d), dims)
+
 """
     length(x::NDArray)
 

test/unittest/ndarray.jl

@@ -770,6 +770,15 @@ function test_show()
   end
 end
 
+function test_size()
+  info("NDArray::size")
+  let A = [1 2; 3 4; 5 6], x = mx.NDArray(A)
+    @test size(A) == size(x)
+    @test size(A, 1, 2, 3, 4, 5) == size(x, 1, 2, 3, 4, 5)
+    @inferred size(x, 1, 2, 3, 4, 5)
+  end
+end  # function test_size()
+
 ################################################################################
 # Run tests
 ################################################################################
@@ -802,6 +811,7 @@ end
   test_fill()
   test_transpose()
   test_show()
+  test_size()
 end
 
 end