clippy: fix len_without_is_empty warnings

src/base/matrix.rs

@@ -298,20 +298,6 @@ impl<N: Scalar, R: Dim, C: Dim, S: Storage<N, R, C>> Matrix<N, R, C, S> {
         unsafe { Self::from_data_statically_unchecked(data) }
     }
 
-    /// The total number of elements of this matrix.
-    ///
-    /// # Examples:
-    ///
-    /// ```
-    /// # use nalgebra::Matrix3x4;
-    /// let mat = Matrix3x4::<f32>::zeros();
-    /// assert_eq!(mat.len(), 12);
-    #[inline]
-    pub fn len(&self) -> usize {
-        let (nrows, ncols) = self.shape();
-        nrows * ncols
-    }
-
     /// The shape of this matrix returned as the tuple (number of rows, number of columns).
     ///
     /// # Examples:

src/base/properties.rs

@@ -10,11 +10,33 @@ use crate::base::storage::Storage;
 use crate::base::{DefaultAllocator, Matrix, Scalar, SquareMatrix};
 
 impl<N: Scalar, R: Dim, C: Dim, S: Storage<N, R, C>> Matrix<N, R, C, S> {
-    /// Indicates if this is an empty matrix.
+    /// The total number of elements of this matrix.
+    ///
+    /// # Examples:
+    ///
+    /// ```
+    /// # use nalgebra::Matrix3x4;
+    /// let mat = Matrix3x4::<f32>::zeros();
+    /// assert_eq!(mat.len(), 12);
+    /// ```
+    #[inline]
+    pub fn len(&self) -> usize {
+        let (nrows, ncols) = self.shape();
+        nrows * ncols
+    }
+
+    /// Returns true if the matrix contains no elements.
+    ///
+    /// # Examples:
+    ///
+    /// ```
+    /// # use nalgebra::Matrix3x4;
+    /// let mat = Matrix3x4::<f32>::zeros();
+    /// assert!(!mat.is_empty());
+    /// ```
     #[inline]
     pub fn is_empty(&self) -> bool {
-        let (nrows, ncols) = self.shape();
-        nrows == 0 || ncols == 0
+        self.len() == 0
     }
 
     /// Indicates if this is a square matrix.

src/base/vec_storage.rs

@@ -85,6 +85,12 @@ impl<N, R: Dim, C: Dim> VecStorage<N, R, C> {
     pub fn len(&self) -> usize {
         self.data.len()
     }
+
+    /// Returns true if the underlying vector contains no elements.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
 }
 
 impl<N, R: Dim, C: Dim> Into<Vec<N>> for VecStorage<N, R, C> {

src/geometry/point.rs

@@ -194,6 +194,19 @@ where
         self.coords.len()
     }
 
+    /// Returns true if the point contains no elements.
+    ///
+    /// # Example
+    /// ```
+    /// # use nalgebra::{Point2, Point3};
+    /// let p = Point2::new(1.0, 2.0);
+    /// assert!(!p.is_empty());
+    /// ```
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
     /// The stride of this point. This is the number of buffer element separating each component of
     /// this point.
     #[inline]

src/linalg/permutation_sequence.rs

@@ -144,6 +144,11 @@ where
         self.len
     }
 
+    /// Returns true if the permutation sequence contains no elements.
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
     /// The determinant of the matrix corresponding to this permutation.
     #[inline]
     pub fn determinant<N: One + ClosedNeg>(&self) -> N {