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Use rvalue subcasting when casting an rvalue container

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This updates the std::tuple, std::pair and `stl.h` type casters to
forward their contained value according to whether the container being
cast is an lvalue or rvalue reference.  This fixes an issue where
subcaster casts were always called with a const lvalue which meant
nested type casters didn't have the desired `cast()` overload invoked.
For example, this caused Eigen values in a tuple to end up with a
readonly flag (issue #935) and made it impossible to return a container
of move-only types (issue #853).

This fixes both issues by adding templated universal reference `cast()`
methods to the various container types that forward container elements
according to the container reference type.
This commit is contained in:
Jason Rhinelander
2017-07-03 19:12:09 -04:00
parent 897d71687e
commit b57281bb00
8 changed files with 144 additions and 35 deletions
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10
tests/test_builtin_casters.cpp
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@@ -86,6 +86,16 @@ TEST_SUBMODULE(builtin_casters, m) {
return std::make_tuple(std::get<2>(input), std::get<1>(input), std::get<0>(input));
}, "Return a triple in reversed order");
m.def("empty_tuple", []() { return std::tuple<>(); });
static std::pair<RValueCaster, RValueCaster> lvpair;
static std::tuple<RValueCaster, RValueCaster, RValueCaster> lvtuple;
static std::pair<RValueCaster, std::tuple<RValueCaster, std::pair<RValueCaster, RValueCaster>>> lvnested;
m.def("rvalue_pair", []() { return std::make_pair(RValueCaster{}, RValueCaster{}); });
m.def("lvalue_pair", []() -> const decltype(lvpair) & { return lvpair; });
m.def("rvalue_tuple", []() { return std::make_tuple(RValueCaster{}, RValueCaster{}, RValueCaster{}); });
m.def("lvalue_tuple", []() -> const decltype(lvtuple) & { return lvtuple; });
m.def("rvalue_nested", []() {
return std::make_pair(RValueCaster{}, std::make_tuple(RValueCaster{}, std::make_pair(RValueCaster{}, RValueCaster{}))); });
m.def("lvalue_nested", []() -> const decltype(lvnested) & { return lvnested; });
// test_builtins_cast_return_none
m.def("return_none_string", []() -> std::string * { return nullptr; });