Created
July 12, 2024 20:14
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| use std::marker::PhantomData; | |
| use std::ptr; | |
| // Behaves like &'a mut dyn FnMut, | |
| // except requires only one pointer indirection for functions without data. | |
| struct ShallowFnMutRef<'a> { | |
| fn_ptr: unsafe fn(*mut ()), | |
| data: *mut (), | |
| _marker: PhantomData<&'a mut ()>, | |
| } | |
| impl<'a> ShallowFnMutRef<'a> { | |
| fn from_closure<F: FnMut()>(f: &'a mut F) -> Self { | |
| unsafe fn call_closure<F: FnMut()>(closure_ptr: *mut ()) { | |
| (&mut*closure_ptr.cast::<F>())(); | |
| } | |
| Self { | |
| fn_ptr: call_closure::<F>, | |
| data: (f as *mut F).cast::<()>(), | |
| _marker: PhantomData, | |
| } | |
| } | |
| fn from_fn<F: Fn() + 'a>(_: F) -> Self { | |
| const { assert!(std::mem::size_of::<F>() == 0) } | |
| fn forward_to_f<F: Fn()>(_: *mut ()) { | |
| let f: F = unsafe { ptr::NonNull::<F>::dangling().as_ptr().read() }; | |
| f(); | |
| } | |
| Self { | |
| fn_ptr: forward_to_f::<F>, | |
| data: ptr::null_mut(), | |
| _marker: PhantomData, | |
| } | |
| } | |
| fn call(&mut self) { | |
| unsafe { (self.fn_ptr)(self.data) } | |
| } | |
| } | |
| fn foo() { | |
| println!("foo called"); | |
| } | |
| fn main() { | |
| let s = String::from("closure called"); | |
| let mut closure = move || println!("{s}"); | |
| ShallowFnMutRef::from_fn(foo).call(); | |
| ShallowFnMutRef::from_closure(&mut closure).call(); | |
| } |
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