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Opt-in Stable Trait VTables #2955

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Opt-in Stable Trait VTables #2955

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f89f810
Add 0000-trait_stable_vtable
chorman0773 Jul 10, 2020
d4394d2
Finish the incomplete summary
chorman0773 Jul 10, 2020
9bbacbd
Make corrections and clarifications to trait_stable_vtable
chorman0773 Jul 16, 2020
2c08a7d
Fix some exposition-only structs
chorman0773 Jul 23, 2020
dae7c08
Add some additional rules for *stable-layout-pointers*
chorman0773 Jul 23, 2020
971c5b6
Add dealloc field
chorman0773 Jul 25, 2020
df86ed2
The dealloc entry is no longer reserved
chorman0773 Jul 25, 2020
37e1992
Add note for compatibility of abi_stable
chorman0773 Jul 25, 2020
cb88439
Fix a minor issue with the general VTable specification
chorman0773 Aug 23, 2020
fdcf8f8
Update
chorman0773 Oct 19, 2020
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2 changes: 1 addition & 1 deletion text/0000-trait_stable_vtable.md
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Expand Up @@ -108,7 +108,7 @@ struct VTable{
size: usize,
align: usize,
drop_in_place: Option<unsafe extern"C" fn(*mut ())->()>,
reserved: *mut ()
dealloc:Option<unsafe extern"C" fn(*mut ())->()>,
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Suggested change
dealloc:Option<unsafe extern"C" fn(*mut ())->()>,
dealloc: Option<unsafe extern "C" fn(*mut ())>,

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For consistency with the other pointers, I'd want to leave the explicit return type. In particular I'd like to have the return type on the virtual fns to show that there is a return type, its just been erased.

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dealloc and drop_in_place don't need an erased return type. For the rest using something like struct ErasedVtableFunction(()); *const ErasedVtableFunction instead would make more sense to prevent accidentally calling it with the wrong signature.

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I think #[repr(transparent)] struct ErasedVTableFn(unsafe extern "C" fn()); ... virtual_fns: [ErasedVTableFn] would be better, since on some targets (MS-DOS is an example, though rust doesn't currently support that target) function pointers and data pointers aren't the same size.

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The type is for exposition-only. The type does not actually exist in the RFC, as part of the core language or standard library. If I actually defined the type, I'd definately put something like enum Empty{} in the parameter list to prevent it being called. The intent is simply to express the layout of the type.

virtual_fns: [unsafe extern "C" fn(*mut ())->()]
}
```
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