internal: add PhantomInvariant and PhantomInvariantLifetime#150
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Currently, the `pin_init` library has an `Invariant` type alias, and it is instantiated using `PhantomData`. Generated code from `pin_data` on the other hand cannot access the crate-local type alias, so it generates `PhantomData<fn(T) -> T>` directly. This is all very inconsistent, despite the exact same use case of ensuring invariance. Add `PhantomInvariant` and `PhantomInvariantLifetime` and switch all users that need to express the concept of invariance to use these. They're polyfills of unstable types in the same names in the Rust standard library. Signed-off-by: Gary Guo <gary@garyguo.net>
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Currently, the
pin_initlibrary has anInvarianttype alias, and it is instantiated usingPhantomData. Generated code frompin_dataon the other hand cannot access the crate-local type alias, so it generatesPhantomData<fn(T) -> T>directly. This is all very inconsistent, despite the exact same use case of ensuring invariance.Add
PhantomInvariantandPhantomInvariantLifetimeand switch all users that need to express the concept of invariance to use these. They're polyfills of unstable types in the same names in the Rust standard library.