Make reference(_internal) the default return value policy for properties #473
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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 pybind#436.
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)`.
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looks good to me, thanks! |
dean0x7d
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Fixes pybind#509. The move policy was already set for rvalues in PR pybind#473, but this only applied to directly cast user-defined types. The problem is that STL containers cast values indirectly and the rvalue information is lost. Therefore the move policy was not set correctly. This commit fixes it. This also makes an additional adjustment to remove the `copy` policy exception: rvalues now always use the `move` policy. This is also safe for copy-only rvalues because the `move` policy has an internal fallback to copying.
wjakob
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Nov 20, 2016
Fixes #509. The move policy was already set for rvalues in PR #473, but this only applied to directly cast user-defined types. The problem is that STL containers cast values indirectly and the rvalue information is lost. Therefore the move policy was not set correctly. This commit fixes it. This also makes an additional adjustment to remove the `copy` policy exception: rvalues now always use the `move` policy. This is also safe for copy-only rvalues because the `move` policy has an internal fallback to copying.
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See #436 for related discussion.
The tests should cover all possible combinations of
def_propery*andreturn_value_policyand make sure the correct overload is chosen:cppfunctionTo make the new default
reference(_internal)policy work correctly for rvalues,type_caster_baseneeded to be tweaked as well. The discussed always-move policy turned into 'almost always'.copywill still be honored if it's selected explicitly. I'm not sure that anyone would actually want to do this (movealready has a fallback for copy-only classes), but I guess it's best not to forbid a valid option. However, all other policies are outright errors for rvalues (pointer to temporary) and therefore cannot be selected.