hphp/hack/src/typing/typing_mutability_env.mli

   1 (**
   2  * Copyright (c) 2017, Facebook, Inc.
   3  * All rights reserved.
   4  *
   5  * This source code is licensed under the MIT license found in the
   6  * LICENSE file in the "hack" directory of this source tree.
   7  *
   8  *)
   9 (* Tracks the different types of mutability of a given local variable
  10   Mutable: Objects marked as mutable must be affine, as in have 0-1 references.
  11   These are mutably owned, so they can be frozen to become immutable. They can
  12   have their properties set, but cannot be assigned to or passed to
  13   immutable contexts.
  14
  15   Borrowed: Mutably borrowed. These can have their properties set, but cannot be
  16   frozen, and have all the same restrictions as mutable variables.
  17   A mutable parameter is always mutably borrowed.
  18
  19   Const: Const types have all the restrictions of immutable vars and mutable
  20   vars. They cannot have their object properties be written toward, and cannot be
  21   reassigned. They are essentially read only.
  22 *)
  23 type mut_type = Mutable | Borrowed | Const
  24 type mutability = Pos.t * mut_type
  25
  26 (* Mapping from local variables to their mutability
  27   Local mutability is stored in the local environment.
  28   Once a variable is frozen, we remove it from the map,
  29   and it is treated like any immutable variable in its
  30   enclosing function.
  31 *)
  32 type mutability_env = mutability Local_id.Map.t
  33
  34 (* Given two mutability maps, intersect them. *)
  35 val intersect_mutability : mutability_env -> mutability_env -> mutability_env -> mutability_env
  36 val to_string : mutability -> string