From ccf22d0d9c368b9df72a2fe125eaf46200e9e0e7 Mon Sep 17 00:00:00 2001
From: James Sharp <james@robin.education>
Date: Fri, 15 Mar 2024 18:35:42 +0000
Subject: [PATCH] Extend err_if_nil

---
 lib/oxide.ex | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/lib/oxide.ex b/lib/oxide.ex
index 8437684..9fdd22d 100644
--- a/lib/oxide.ex
+++ b/lib/oxide.ex
@@ -184,17 +184,26 @@ defmodule Oxide.Result do
   @doc ~S"""
   Convert a maybe-nil value to a result.
 
-  Maps `nil` to `{:error, reason}` and any non-`nil` value to `{:ok, value}`.
+  Maps `nil` and `{:ok, nil}` to `{:error, reason}`, passes errors through and otherwise maps `value`, or {:ok, value}` to `{:ok, value}`.
 
       iex> %{"key" => "value"} |> Map.get("key") |> Result.err_if_nil(:notfound)
       {:ok, "value"}
       iex> %{"key" => "value"} |> Map.get("missing") |> Result.err_if_nil(:notfound)
       {:error, :notfound}
+      iex> {:ok, nil} |> Result.err_if_nil(:notfound)
+      {:error, :notfound}
+      iex> {:ok, "value"} |> Result.err_if_nil(:notfound)
+      {:ok, "value"}
+      iex> {:error, :badthing} |> Result.err_if_nil(:notfound)
+      {:error, :badthing}
 
   """
   @spec err_if_nil(any(), any()) :: t()
   def err_if_nil(value, reason)
   def err_if_nil(value, reason) when is_nil(value), do: {:error, reason}
+  def err_if_nil({:ok, value}, reason) when is_nil(value), do: {:error, reason}
+  def err_if_nil({:ok, value}, _reason) when not is_nil(value), do: {:ok, value}
+  def err_if_nil({:error, reason}, _reason), do: {:error, reason}
   def err_if_nil(value, _reason) when not is_nil(value), do: {:ok, value}
 
   @doc ~S"""