/-
Copyright (c) 2024 Lean FRO. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Henrik Böving
-/
module

prelude
public import Init.Data.List.Basic

public section

set_option linter.listVariables true -- Enforce naming conventions for `List`/`Array`/`Vector` variables.
set_option linter.indexVariables true -- Enforce naming conventions for index variables.

/--
Auxiliary definition for `List.toArray`.
`List.toArrayAux as r = r ++ as.toArray`
-/
@[inline_if_reduce]
def List.toArrayAux : List α → Array α → Array α
  | nil,       xs => xs
  | cons a as, xs => toArrayAux as (xs.push a)

/--
Converts a `List α` into an `Array α` by repeatedly pushing elements from the list onto an empty
array. `O(|xs|)`.

Use `List.toArray` instead of calling this function directly. At runtime, this operation implements
both `List.toArray` and `Array.mk`.
-/
-- This function is exported to C, where it is called by `Array.mk`
-- (the constructor) to implement this functionality.
@[inline, expose, match_pattern, pp_nodot, export lean_list_to_array]
def List.toArrayImpl (xs : List α) : Array α :=
  xs.toArrayAux (Array.mkEmpty xs.length)