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Documented new conversion facilities; went into a little more detail.

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[SVN r8180]
This commit is contained in:
Dave Abrahams
2000-11-12 20:50:48 +00:00
parent 2dc27af335
commit fed2ef5d64
1 changed files with 43 additions and 17 deletions
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enums.html
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@@ -11,18 +11,44 @@
<p>Because there is in general no way to deduce that a value of arbitrary type T
is an enumeration constant, py_cpp cannot automatically convert enum values to
and from Python. To handle this case, you need to decide how you want the enum
to show up in Python (since Python doesn't have enums). If you are satisfied
with a Python int as a way to represent your enum values, you can write some
simple <code>from_python()</code> and <code>to_python()</code> functions in
<code>namespace py::</code>
to show up in Python (since Python doesn't have enums). Once you have done that,
you can write some simple <code>from_python()</code> and
<code>to_python()</code> functions.
<blockquote><pre>
#ifndef PY_NO_INLINE_FRIENDS_IN_NAMESPACE // workaround GCC 2.95.2 bug
<p>If you are satisfied with a Python int as a way to represent your enum
values, py_cpp provides a shorthand for these functions. You just need to
instantiate <code>py::enum_as_int_converters&lt;EnumType&gt;</code> where
<code>EnumType</code> is your enumerated type. There are two convenient ways to do this:
<ol>
<li><blockquote>
<pre>
// drop into namespace py and explicitly instantiate
namespace py {
#endif
template class enum_as_int_converters<extclass_demo::EnumOwner::enum_type>;
}
</pre>
</blockquote>
<li><blockquote><pre>
// instantiate as base class in any namespace
struct EnumTypeConverters
: py::py_enum_as_int_converters<EnumType>
{
};
</blockquote></pre>
</ol>
MyEnumType from_python(PyObject* x,
py::Type&lt;MyEnumType&gt;)
<p>Either of the above is equivalent to the following declarations:
<blockquote><pre>
PY_BEGIN_CONVERSION_NAMESPACE // this is a gcc 2.95.2 bug workaround
MyEnumType from_python(PyObject* x, py::Type&lt;MyEnumType&gt;)
{
return static_cast&lt;MyEnum&gt;(
from_python(x, py::Type&lt;long&gt;()));
}
MyEnumType from_python(PyObject* x, py::Type&lt;const MyEnumType&amp;&gt;)
{
return static_cast&lt;MyEnum&gt;(
from_python(x, py::Type&lt;long&gt;()));
@@ -32,13 +58,10 @@ namespace py {
{
return to_python(static_cast&lt;long&gt;(x));
}
#ifndef PY_NO_INLINE_FRIENDS_IN_NAMESPACE
}
#endif
PY_END_CONVERSION_NAMESPACE
</pre></blockquote>
This technique defines the conversions of
<p>This technique defines the conversions of
<code>MyEnumType</code> in terms of the conversions for the built-in
<code>long</code> type.
@@ -50,7 +73,10 @@ mymodule.add(py::to_python(enum_value_1), "enum_value_1");
mymodule.add(py::to_python(enum_value_2), "enum_value_2");
...
</pre></blockquote>
You can also add these to an extension class definition:
You can also add these to an extension class definition, if your enum happens to
be local to a class and you want the analogous interface in Python:
<blockquote><pre>
my_class.add(py::to_python(enum_value_1), "enum_value_1");
my_class.add(py::to_python(enum_value_2), "enum_value_2");
@@ -63,6 +89,6 @@ my_class.add(py::to_python(enum_value_2), "enum_value_2");
express or implied warranty, and with no claim as to its suitability
for any purpose.
<p>
Updated: Nov 5, 2000
Updated: Nov 12, 2000
</div>