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switch template bool specialization order

release/4.3a0
Gerry Chen 2021-12-03 06:46:26 -05:00
parent ba3cc85701
commit ddcca4cdae
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1 changed files with 16 additions and 15 deletions
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31
gtsam/nonlinear/NonlinearFactor.h
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@ -314,7 +314,8 @@ public:
* *
* The tricky part is that we want to _conditionally_ alias these only if the * The tricky part is that we want to _conditionally_ alias these only if the
* `sizeof...(VALUES)` is greater than the index we want to alias (e.g. a 3-way * `sizeof...(VALUES)` is greater than the index we want to alias (e.g. a 3-way
* factor should only have up to X3). * factor should only have up to X3). SFINAE doesn't work in this case with
* aliases so we have to come up with a different approach.
* *
* The approach we use is to create structs which use template specialization to * The approach we use is to create structs which use template specialization to
* conditionally typedef X1, X2, ... for us, then inherit from them to inherit * conditionally typedef X1, X2, ... for us, then inherit from them to inherit
@ -345,26 +346,26 @@ namespace detail {
// First handle `typedef X`. By default, we do not alias X (empty struct). // First handle `typedef X`. By default, we do not alias X (empty struct).
template <bool, class... VALUES> template <bool, class... VALUES>
struct AliasX_ {}; struct AliasX_ {};
// But if `1 == sizeof...(VALUES)` is true, then we do alias X by specializing // But if the first template is true, then we do alias X by specializing.
// for when the first template parameter is true.
template <class... VALUES> template <class... VALUES>
struct AliasX_<(1 == sizeof...(VALUES)), VALUES...> { struct AliasX_<true, VALUES...> {
using X = GET_VALUE_I(VALUES, 0); using X = GET_VALUE_I(VALUES, 0);
}; };
// We'll alias the "true" template version for convenience. // We'll alias (for convenience) the correct version based on whether or not
// `1 == sizeof...(VALUES)` is true
template <class... VALUES> template <class... VALUES>
using AliasX = AliasX_<true, VALUES...>; using AliasX = AliasX_<(1 == sizeof...(VALUES)), VALUES...>;
// Now do the same thing for X1, X2, ... using a macro. // Now do the same thing for X1, X2, ... using a macro.
#define ALIAS_HELPER_X(N) \ #define ALIAS_HELPER_X(N) \
template <bool, class... VALUES> \ template <bool, class... VALUES> \
struct AliasX##N##_ {}; \ struct AliasX##N##_ {}; \
template <class... VALUES> \ template <class... VALUES> \
struct AliasX##N##_<(N <= sizeof...(VALUES)), VALUES...> { \ struct AliasX##N##_<true, VALUES...> { \
using X##N = GET_VALUE_I(VALUES, N - 1); \ using X##N = GET_VALUE_I(VALUES, N - 1); \
}; \ }; \
template <class... VALUES> \ template <class... VALUES> \
using AliasX##N = AliasX##N##_<true, VALUES...>; using AliasX##N = AliasX##N##_<(N <= sizeof...(VALUES)), VALUES...>;
ALIAS_HELPER_X(1); ALIAS_HELPER_X(1);
ALIAS_HELPER_X(2); ALIAS_HELPER_X(2);
ALIAS_HELPER_X(3); ALIAS_HELPER_X(3);