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25 lines
781 B
25 lines
781 B
5 years ago
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(*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*)
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open! IStd
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type t =
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| Nullable (** No guarantees on the nullability *)
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| Nonnull
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(** We believe that this value can not be null. If it is not the case, this is
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an unsoundness issue for Nullsafe, and we aim to minimize number of such issues
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occuring in real-world programs. *)
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[@@deriving compare, equal]
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let join x y =
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match (x, y) with Nullable, _ | _, Nullable -> Nullable | Nonnull, Nonnull -> Nonnull
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let is_subtype ~subtype ~supertype = equal (join subtype supertype) supertype
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let to_string = function Nullable -> "Nullable" | Nonnull -> "Nonnull"
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