document LvalueBit better

1 files changed, 6 insertions, 1 deletions

diff --git a/Eigen/src/Core/DenseCoeffsBase.h b/Eigen/src/Core/DenseCoeffsBase.h
index 9de9ae280..b4dbe1d95 100644
--- a/Eigen/src/Core/DenseCoeffsBase.h
+++ b/Eigen/src/Core/DenseCoeffsBase.h
@@ -44,6 +44,11 @@ class DenseCoeffsBase<Derived,ReadOnlyAccessors> : public EigenBase<Derived>
     typedef typename internal::traits<Derived>::Index Index;
     typedef typename internal::traits<Derived>::Scalar Scalar;
     typedef typename internal::packet_traits<Scalar>::type PacketScalar;
+
+    // explanation for this CoeffReturnType typedef.
+    // this is the return type of the coeff() method.
+    // The LvalueBit means exactly that we can offer a coeffRef() method, which means exactly that we can get references
+    // to coeffs, which means exactly that we can have coeff() return a const reference (as opposed to returning a value).
     typedef typename internal::conditional<bool(internal::traits<Derived>::Flags&LvalueBit),
                                 const Scalar&,
                                 typename internal::conditional<internal::is_arithmetic<Scalar>::value, Scalar, const Scalar>::type
@@ -230,7 +235,7 @@ class DenseCoeffsBase<Derived,ReadOnlyAccessors> : public EigenBase<Derived>
 
   protected:
     // explanation: DenseBase is doing "using ..." on the methods from DenseCoeffsBase.
-    // But some methods are only available in the EnableDirectAccessAPI case.
+    // But some methods are only available in the DirectAccess case.
     // So we add dummy methods here with these names, so that "using... " doesn't fail.
     // It's not private so that the child class DenseBase can access them, and it's not public
     // either since it's an implementation detail, so has to be protected.