Remove phantom data from matrix debug output

Addresses #295.

src/core/matrix.rs

@@ -68,7 +68,7 @@ pub type MatrixCross<N, R1, C1, R2, C2> =
 /// dynamically-sized column vector should be represented as a `Matrix<N, Dynamic, U1, S>` (given
 /// some concrete types for `N` and a compatible data storage type `S`).
 #[repr(C)]
-#[derive(Hash, Debug, Clone, Copy)]
+#[derive(Hash, Clone, Copy)]
 pub struct Matrix<N: Scalar, R: Dim, C: Dim, S> {
     /// The data storage that contains all the matrix components and informations about its number
     /// of rows and column (if needed).
@@ -77,6 +77,14 @@ pub struct Matrix<N: Scalar, R: Dim, C: Dim, S> {
     _phantoms: PhantomData<(N, R, C)>
 }
 
+impl<N: Scalar, R: Dim, C: Dim, S: fmt::Debug> fmt::Debug for Matrix<N, R, C, S> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        formatter.debug_struct("Matrix")
+            .field("data", &self.data)
+            .finish()
+    }
+}
+
 #[cfg(feature = "serde-serialize")]
 impl<N, R, C, S> Serialize for Matrix<N, R, C, S>
     where N: Scalar,

tests/core/matrix.rs

@@ -62,6 +62,13 @@ fn iter() {
     assert!(it.next().is_none());
 }
 
+#[test]
+fn debug_output_corresponds_to_data_container() {
+    assert_eq!(
+        format!("{:?}", Matrix2::new(1.0, 2.0, 3.0, 4.0)),
+        "Matrix { data: [1, 3, 2, 4] }"
+    );
+}
 
 #[test]
 fn is_column_major() {