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Make Eigen::Map<const Vector>::operator[] return correct type

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AnonymousPC 2025-06-07 03:15:18 +08:00 committed by Antonio Sánchez
parent d0b490ee09
commit cda19a6255
1 changed files with 7 additions and 1 deletions
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8
Eigen/src/Core/DenseCoeffsBase.h
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@ -45,10 +45,16 @@ class DenseCoeffsBase<Derived, ReadOnlyAccessors> : public EigenBase<Derived> {
// - 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 DirectAccessBit means exactly that the underlying data of coefficients can be directly accessed as a plain
// strided array, which means exactly that the underlying data of coefficients does exist in memory, which means
// exactly that the coefficients is const-referencable, which means exactly that we can have coeff() return a const
// reference. For example, Map<const Matrix> have DirectAccessBit but not LvalueBit, so that Map<const Matrix>.coeff()
// does points to a const Scalar& which exists in memory, while does not allow coeffRef() as it would not provide a
// lvalue. Notice that DirectAccessBit and LvalueBit are mutually orthogonal.
// - The is_arithmetic 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 std::conditional_t<bool(internal::traits<Derived>::Flags& LvalueBit), const Scalar&,
typedef std::conditional_t<bool(internal::traits<Derived>::Flags&(LvalueBit | DirectAccessBit)), const Scalar&,
std::conditional_t<internal::is_arithmetic<Scalar>::value, Scalar, const Scalar>>
CoeffReturnType;