From aef59c42eb4de428bcb608cde8fbfd6c292e0797 Mon Sep 17 00:00:00 2001
From: Mark Spanbroek <mark@spanbroek.net>
Date: Thu, 18 Mar 2021 09:50:06 +0100
Subject: [PATCH] Allow optional binding to vars

---
 questionable/options.nim     |  9 +++++++++
 questionable/results.nim     |  9 +++++++++
 testmodules/options/test.nim | 13 +++++++++++++
 testmodules/result/test.nim  | 13 +++++++++++++
 4 files changed, 44 insertions(+)

diff --git a/questionable/options.nim b/questionable/options.nim
index eb9c3d5..19a5603 100644
--- a/questionable/options.nim
+++ b/questionable/options.nim
@@ -1,4 +1,5 @@
 import std/options
+import std/macros
 import ./chaining
 import ./operators
 
@@ -26,6 +27,14 @@ template `=?`*[T](name: untyped{nkIdent}, option: ?T): bool =
   template name: T {.used.} = option.unsafeGet()
   option.isSome
 
+macro `=?`*[T](variable: untyped{nkVarTy}, option: ?T): bool =
+  let name = variable[0]
+  quote do:
+    var `name` : typeof(`option`.unsafeGet())
+    if `option`.isSome:
+      `name` = `option`.unsafeGet()
+    `option`.isSome
+
 template `|?`*[T](option: ?T, fallback: T): T =
   if option.isSome:
     option.unsafeGet()
diff --git a/questionable/results.nim b/questionable/results.nim
index 58255f0..6def9f6 100644
--- a/questionable/results.nim
+++ b/questionable/results.nim
@@ -1,3 +1,4 @@
+import std/macros
 import ./resultsbase
 import ./options
 import ./operators
@@ -41,6 +42,14 @@ template `=?`*[T](name: untyped{nkIdent}, value: ?!T): bool =
   template name: T {.used.} = value.unsafeGet()
   value.isOk
 
+macro `=?`*[T](variable: untyped{nkVarTy}, option: ?!T): bool =
+  let name = variable[0]
+  quote do:
+    var `name` : typeof(`option`.unsafeGet())
+    if `option`.isOk:
+      `name` = `option`.unsafeGet()
+    `option`.isOk
+
 proc option*[T,E](value: Result[T,E]): ?T =
   if value.isOk:
     value.unsafeGet.some
diff --git a/testmodules/options/test.nim b/testmodules/options/test.nim
index 21afd33..8003e6b 100644
--- a/testmodules/options/test.nim
+++ b/testmodules/options/test.nim
@@ -74,6 +74,19 @@ suite "optionals":
     if a =? a:
       check a == 42
 
+  test "=? works with var":
+    if var a =? 1.some and var b =? 2.some:
+      check a == 1
+      inc a
+      check a == b
+      inc b
+      check b == 3
+    else:
+      fail
+
+    if var a =? int.none:
+      fail
+
   test "unary operator `-` works for options":
     check -(-42.some) == 42.some
     check -(int.none) == int.none
diff --git a/testmodules/result/test.nim b/testmodules/result/test.nim
index cdbdf5b..0af83ad 100644
--- a/testmodules/result/test.nim
+++ b/testmodules/result/test.nim
@@ -78,6 +78,19 @@ suite "result":
     if a =? a:
       check a == 42
 
+  test "=? works with var":
+    if var a =? 1.success and var b =? 2.success:
+      check a == 1
+      inc a
+      check a == b
+      inc b
+      check b == 3
+    else:
+      fail
+
+    if var a =? int.failure(error):
+      fail
+
   test "catch can be used to convert exceptions to results":
     check parseInt("42").catch == 42.success
     check parseInt("foo").catch.error of ValueError