From 574416b8428756c9fc52e79fc00a2402d1a4e59c Mon Sep 17 00:00:00 2001
From: Benoit Jacob <jacob.benoit.1@gmail.com>
Date: Fri, 20 Jun 2008 15:26:39 +0000
Subject: [PATCH] Override MatrixBase::eval() since matrices don't need to be
 evaluated, it is enough to just read them.

---
 Eigen/src/Core/Matrix.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Eigen/src/Core/Matrix.h b/Eigen/src/Core/Matrix.h
index e14999445..11fadf49b 100644
--- a/Eigen/src/Core/Matrix.h
+++ b/Eigen/src/Core/Matrix.h
@@ -336,6 +336,14 @@ class Matrix : public MatrixBase<Matrix<_Scalar, _Rows, _Cols, _MaxRows, _MaxCol
     }
     /** Destructor */
     inline ~Matrix() {}
+
+    /** Override MatrixBase::eval() since matrices don't need to be evaluated, it is enough to just read them.
+      * This prevents a useless copy when doing e.g. "m1 = m2.eval()"
+      */
+    const Matrix& eval() const
+    {
+      return *this;
+    }
 };
 
 #define EIGEN_MAKE_TYPEDEFS(Type, TypeSuffix, Size, SizeSuffix) \