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Added a comment on why is_arithmetic is used in DenseCoeffsBase.

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This commit is contained in:
Hauke Heibel 2010-11-02 10:11:22 +01:00
parent 96e4a4b59c
commit b3007db131
1 changed files with 6 additions and 3 deletions
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9
Eigen/src/Core/DenseCoeffsBase.h
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@ -45,10 +45,13 @@ class DenseCoeffsBase<Derived,ReadOnlyAccessors> : public EigenBase<Derived>
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
// 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).
// - The is_artihmetic check is required since "const int", "const double", etc. will cause warnings on some systems
// while the declaration of "const T", where T is a non arithmetic type does not. Always returning "const Scalar&" is
// not possible, since the underlying expressions might not offer a valid address the reference could be referring to.
typedef typename internal::conditional<bool(internal::traits<Derived>::Flags&LvalueBit),
const Scalar&,
typename internal::conditional<internal::is_arithmetic<Scalar>::value, Scalar, const Scalar>::type