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Make reference(_internal) the default return value policy for properties (#473)

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* Make reference(_internal) the default return value policy for properties

Before this, all `def_property*` functions used `automatic` as their
default return value policy. This commit makes it so that:

 * Non-static properties use `reference_interal` by default, thus
   matching `def_readonly` and `def_readwrite`.

 * Static properties use `reference` by default, thus matching
   `def_readonly_static` and `def_readwrite_static`.

In case `cpp_function` is passed to any `def_property*`, its policy will
be used instead of any defaults. User-defined arguments in `extras`
still have top priority and will override both the default policies and
the ones from `cpp_function`.

Resolves #436.

* Almost always use return_value_policy::move for rvalues

For functions which return rvalues or rvalue references, the only viable
return value policies are `copy` and `move`. `reference(_internal)` and
`take_ownership` would take the address of a temporary which is always
an error.

This commit prevents possible user errors by overriding the bad rvalue
policies with `move`. Besides `move`, only `copy` is allowed, and only
if it's explicitly selected by the user.

This is also a necessary safety feature to support the new default
return value policies for properties: `reference(_internal)`.
This commit is contained in:
Dean Moldovan
2016-11-01 11:44:57 +01:00
committed by Wenzel Jakob
parent 030d10e826
commit 03f627ebb1
6 changed files with 128 additions and 8 deletions
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44
tests/test_methods_and_attributes.cpp
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@@ -66,6 +66,24 @@ struct TestProperties {
int TestProperties::static_value = 1;
struct SimpleValue { int value = 1; };
struct TestPropRVP {
SimpleValue v1;
SimpleValue v2;
static SimpleValue sv1;
static SimpleValue sv2;
const SimpleValue &get1() const { return v1; }
const SimpleValue &get2() const { return v2; }
SimpleValue get_rvalue() const { return v2; }
void set1(int v) { v1.value = v; }
void set2(int v) { v2.value = v; }
};
SimpleValue TestPropRVP::sv1{};
SimpleValue TestPropRVP::sv2{};
class DynamicClass {
public:
DynamicClass() { print_default_created(this); }
@@ -117,6 +135,32 @@ test_initializer methods_and_attributes([](py::module &m) {
[](py::object) { return TestProperties::static_get(); },
[](py::object, int v) { return TestProperties::static_set(v); });
py::class_<SimpleValue>(m, "SimpleValue")
.def_readwrite("value", &SimpleValue::value);
auto static_get1 = [](py::object) -> const SimpleValue & { return TestPropRVP::sv1; };
auto static_get2 = [](py::object) -> const SimpleValue & { return TestPropRVP::sv2; };
auto static_set1 = [](py::object, int v) { TestPropRVP::sv1.value = v; };
auto static_set2 = [](py::object, int v) { TestPropRVP::sv2.value = v; };
auto rvp_copy = py::return_value_policy::copy;
py::class_<TestPropRVP>(m, "TestPropRVP")
.def(py::init<>())
.def_property_readonly("ro_ref", &TestPropRVP::get1)
.def_property_readonly("ro_copy", &TestPropRVP::get2, rvp_copy)
.def_property_readonly("ro_func", py::cpp_function(&TestPropRVP::get2, rvp_copy))
.def_property("rw_ref", &TestPropRVP::get1, &TestPropRVP::set1)
.def_property("rw_copy", &TestPropRVP::get2, &TestPropRVP::set2, rvp_copy)
.def_property("rw_func", py::cpp_function(&TestPropRVP::get2, rvp_copy), &TestPropRVP::set2)
.def_property_readonly_static("static_ro_ref", static_get1)
.def_property_readonly_static("static_ro_copy", static_get2, rvp_copy)
.def_property_readonly_static("static_ro_func", py::cpp_function(static_get2, rvp_copy))
.def_property_static("static_rw_ref", static_get1, static_set1)
.def_property_static("static_rw_copy", static_get2, static_set2, rvp_copy)
.def_property_static("static_rw_func", py::cpp_function(static_get2, rvp_copy), static_set2)
.def_property_readonly("rvalue", &TestPropRVP::get_rvalue)
.def_property_readonly_static("static_rvalue", [](py::object) { return SimpleValue(); });
py::class_<DynamicClass>(m, "DynamicClass", py::dynamic_attr())
.def(py::init());