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with_custodian_and_ward explanation
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== with_custodian_and_ward == ties lifetimes of the arguments |
== with_custodian_and_ward<M,N> == Ties lifetimes of the arguments. Use of template parameters M,N: * 0 - result * 1 - 1st argument (self for method calls) * 2 - 2nd argument (1st for method calls) Keeps N-th argument as long as M-th is alive. For example, container operation ''append'' usualy uses ''with_custodian_and_ward<1,2>'' which means keep argument alive with container itself is alive. |
CallPolicy allows ["boost.python"] to deal with raw references and pointers. Different policies specifies different strategies of managing object ownership.
with_custodian_and_ward<M,N>
Ties lifetimes of the arguments.
Use of template parameters M,N:
- 0 - result
- 1 - 1st argument (self for method calls)
- 2 - 2nd argument (1st for method calls)
Keeps N-th argument as long as M-th is alive.
For example, container operation append usualy uses with_custodian_and_ward<1,2> which means keep argument alive with container itself is alive.
with_custodian_and_ward_postcall
ties lifetimes of the arguments and results
return_internal_reference
Builds a Python object around a pointer to the C++ result object (which must have a class_<> wrapper somewhere), and applies some lifetime management to keep the "self" object alive as long as the Python result is alive.
return_value_policy<T>
with T one of:
reference_existing_object
naïve (dangerous) approach
["boost.python/ResultConverterGenerator"] which can be used to wrap C++ functions returning a reference or pointer to a C++ object.
When the wrapped function is called, the value referenced by its return value is not copied. BR A new Python object is created which contains an unowned U* pointer to the referent of the wrapped function's return value, and no attempt is made to ensure that the lifetime of the referent is at least as long as that of the corresponding Python object.
This class is used in the implementation of return_internal_reference.
copy_non_const_reference
copy_const_reference
BoostPython v1 approach
manage_new_object
BoostPython/ResultConverterGenerator which can be used to wrap C++ functions returning a pointer to an object allocated with a new-expression and expecting the caller to take responsibility for deleting that C++ object from heap. ["boost.python"] will do it as part of Python object destruction.
Use case:
T* factory() { return new T(); } class_<T>("T"); def("Tfactory", factory, return_value_policy<manage_new_object>() );
return_by_value
["boost.python/ResultConverterGenerator"] which can be used to wrap C++ functions returning any reference or value type.BR The return value is copied into a new Python object.