mirror of
https://github.com/pocketpy/pocketpy
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138 lines
4.1 KiB
Markdown
138 lines
4.1 KiB
Markdown
---
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icon: dot
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label: 'Bind native function'
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order: 60
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---
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pkpy allows to wrap a function pointer as a python function or method that can be called in python code.
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This function pointer has the following signature:
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```cpp
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typedef PyObject* (*NativeFuncC)(VM*, ArgsView);
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```
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+ The first argument is the pointer of `VM` instance.
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+ The second argument is an array-like object indicates the arguments list. You can use `[]` operator to get the element.
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+ The return value is a `PyObject*`, which should not be `nullptr`. If there is no return value, return `vm->None`.
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!!!
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Native functions do not support keyword arguments.
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!!!
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### Bind a function
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Assume you have a cpp function `bool equals(int a, int b)`.
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```cpp
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bool equals(int a, int b){
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return a == b;
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}
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```
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You can bind it into `test.equals` by using `vm->bind_func<ARGC>`:
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```cpp
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PyObject* obj = vm->new_module("test");
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// v [function name]
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vm->bind_func<2>(obj, "equals", [](VM* vm, ArgsView args){
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// ^ argument count
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int a = CAST(int, args[0]);
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int b = CAST(int, args[1]);
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bool result = equals(a, b);
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return VAR(result);
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});
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```
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+ The first argument is the target object to bind. It can be any python object with an instance dict, such as a module, a class, or an instance.
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+ The second argument is the function name.
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+ The third argument is the function pointer. We often use lambda expression to wrap it. A non-capturing lambda expression can be converted to a function pointer.
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The template argument `ARGC` is the argument count of the function. If the function is variadic, use `-1` as the argument count.
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The interpreter will ensure `args.size() == ARGC` and throws `TypeError` if not.
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For variadic functions, you need to check `args.size()` manually.
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If you want to bind a function into `builtins` module, use `vm->bind_builtin_func<ARGC>` instead.
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### Bind a constructor
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The constructor of a class is a special function that returns an instance of the class.
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It corresponds to the `__new__` magic method in python (not `__init__`).
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```cpp
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vm->bind_constructor<3>(type, [](VM* vm, ArgsView args){
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float x = CAST_F(args[1]);
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float y = CAST_F(args[2]);
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return VAR(Vec2(x, y));
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});
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```
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### Bind a method
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The `vm->bind_method<ARGC>` usage is almost the same as `vm->bind_func<ARGC>`.
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The only difference is that `ARGC` in `vm->bind_method<ARGC>` does not include the `self` argument.
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```cpp
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vm->bind_method<1>("int", "equals", [](VM* vm, ArgsView args){
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int self = CAST(int, args[0]);
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int other = CAST(int, args[1]);
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return VAR(self == other);
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});
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```
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### Bind a magic method
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For some magic methods, we provide specialized binding function.
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They do not take universal function pointer as argument.
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You need to provide the detailed `Type` object and the corresponding function pointer.
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```cpp
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PyObject* __add__(PyObject* lhs, PyObject* rhs){
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int a = CAST(int, lhs);
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int b = CAST(int, rhs);
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return VAR(a + b);
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}
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Type type = vm->tp_int;
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vm->bind__add__(type, __add__);
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```
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This specialized binding function has optimizations and result in better performance when calling from python code.
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For example, `vm->bind__add__` is preferred over `vm->bind_method<1>(type, "__add__", ...)`.
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### Bind a property
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a property is a python's `property` that attached to a type instance with a getter and an optional setter. It is a data descriptor. A property redirects attribute access to specific functions.
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You can use `@property` to create python property or use `vm->property` to create native property.
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```cpp
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struct Point {
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PY_CLASS(Point, test, Point);
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int x;
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int y;
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Point(int x, int y) : x(x), y(y) {}
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static void _register(VM *vm, auto mod, auto type) {
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vm->bind_constructor<3>(type, [](VM *vm, auto args) {
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auto x = CAST(i64, args[1]);
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auto y = CAST(i64, args[2]);
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return VAR_T(Point, x, y);
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});
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// getter and setter of property `x`
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type->attr().set("x", vm->property([](VM* vm, ArgsView args){
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Point& self = CAST(Point&, args[0]);
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return VAR(self.x);
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},
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[](VM* vm, ArgsView args){
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Point& self = CAST(Point&, args[0]);
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self.x = CAST(int, args[1]);
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return vm->None;
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}));
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}
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};
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``` |