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Remove deprecated placement-new constructor from docs

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Dean Moldovan 2017-09-05 16:49:33 +02:00
parent a80af9557d
commit 0991d7fba1
1 changed files with 5 additions and 37 deletions
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docs/advanced/classes.rst
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@ -361,14 +361,8 @@ Custom constructors
The syntax for binding constructors was previously introduced, but it only The syntax for binding constructors was previously introduced, but it only
works when a constructor of the appropriate arguments actually exists on the works when a constructor of the appropriate arguments actually exists on the
C++ side. To extend this to more general cases, pybind11 offers two different C++ side. To extend this to more general cases, pybind11 makes it possible
approaches: binding factory functions, and placement-new creation. to bind factory functions as constructors. For example, suppose you have a
Factory function constructors
-----------------------------
It is possible to expose a Python-side constructor from a C++ function that
returns a new object by value or pointer. For example, suppose you have a
class like this: class like this:
.. code-block:: cpp .. code-block:: cpp
@ -381,6 +375,9 @@ class like this:
static Example create(int a) { return Example(a); } static Example create(int a) { return Example(a); }
}; };
py::class_<Example>(m, "Example")
.def(py::init(&Example::create));
While it is possible to create a straightforward binding of the static While it is possible to create a straightforward binding of the static
``create`` method, it may sometimes be preferable to expose it as a constructor ``create`` method, it may sometimes be preferable to expose it as a constructor
on the Python side. This can be accomplished by calling ``.def(py::init(...))`` on the Python side. This can be accomplished by calling ``.def(py::init(...))``
@ -463,35 +460,6 @@ an alias:
.def(py::init([]() { return new PyExample(); })) .def(py::init([]() { return new PyExample(); }))
; ;
Low-level placement-new construction
------------------------------------
A second approach for creating new instances use C++ placement new to construct
an object in-place in preallocated memory. To do this, you simply bind a
method name ``__init__`` that takes the class instance as the first argument by
pointer or reference, then uses a placement-new constructor to construct the
object in the pre-allocated (but uninitialized) memory.
For example, instead of:
.. code-block:: cpp
py::class_<Example>(m, "Example")
.def(py::init<int>());
you could equivalently write:
.. code-block:: cpp
py::class_<Example>(m, "Example")
.def("__init__",
[](Example &instance, int arg) {
new (&instance) Example(arg);
}
);
which will invoke the constructor in-place at the pre-allocated memory.
Brace initialization Brace initialization
-------------------- --------------------