From c08f9311bf52bab5f94539663a05e091e55e3e24 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Tue, 25 Feb 2025 20:14:13 +0800
Subject: [PATCH] fixes #24720; std lib iterators unnecessarily require value
 copies

---
 lib/pure/collections/tables.nim | 12 ++++++------
 tests/arc/t24720.nim            | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+), 6 deletions(-)
 create mode 100644 tests/arc/t24720.nim

diff --git a/lib/pure/collections/tables.nim b/lib/pure/collections/tables.nim
index 082e1e96f5591..dc123d25d5873 100644
--- a/lib/pure/collections/tables.nim
+++ b/lib/pure/collections/tables.nim
@@ -677,7 +677,7 @@ template withValue*[A, B](t: var Table[A, B], key: A,
     body2
 
 
-iterator pairs*[A, B](t: Table[A, B]): (A, B) =
+iterator pairs*[A, B](t: Table[A, B]): (lent A, lent B) =
   ## Iterates over any `(key, value)` pair in the table `t`.
   ##
   ## See also:
@@ -1139,7 +1139,7 @@ proc `==`*[A, B](s, t: TableRef[A, B]): bool =
 
 
 
-iterator pairs*[A, B](t: TableRef[A, B]): (A, B) =
+iterator pairs*[A, B](t: TableRef[A, B]): (lent A, lent B) =
   ## Iterates over any `(key, value)` pair in the table `t`.
   ##
   ## See also:
@@ -1727,7 +1727,7 @@ proc `==`*[A, B](s, t: OrderedTable[A, B]): bool =
 
 
 
-iterator pairs*[A, B](t: OrderedTable[A, B]): (A, B) =
+iterator pairs*[A, B](t: OrderedTable[A, B]): (lent A, lent B) =
   ## Iterates over any `(key, value)` pair in the table `t` in insertion
   ## order.
   ##
@@ -2150,7 +2150,7 @@ proc `==`*[A, B](s, t: OrderedTableRef[A, B]): bool =
 
 
 
-iterator pairs*[A, B](t: OrderedTableRef[A, B]): (A, B) =
+iterator pairs*[A, B](t: OrderedTableRef[A, B]): (lent A, lent B) =
   ## Iterates over any `(key, value)` pair in the table `t` in insertion
   ## order.
   ##
@@ -2564,7 +2564,7 @@ proc `==`*[A](s, t: CountTable[A]): bool =
   equalsImpl(s, t)
 
 
-iterator pairs*[A](t: CountTable[A]): (A, int) =
+iterator pairs*[A](t: CountTable[A]): (lent A, int) =
   ## Iterates over any `(key, value)` pair in the table `t`.
   ##
   ## See also:
@@ -2845,7 +2845,7 @@ proc `==`*[A](s, t: CountTableRef[A]): bool =
   else: result = s[] == t[]
 
 
-iterator pairs*[A](t: CountTableRef[A]): (A, int) =
+iterator pairs*[A](t: CountTableRef[A]): (lent A, int) =
   ## Iterates over any `(key, value)` pair in the table `t`.
   ##
   ## See also:
diff --git a/tests/arc/t24720.nim b/tests/arc/t24720.nim
new file mode 100644
index 0000000000000..9f4eb2f698e61
--- /dev/null
+++ b/tests/arc/t24720.nim
@@ -0,0 +1,20 @@
+discard """
+  matrix: "--mm:orc"
+  output: '''
+found entry
+'''
+"""
+
+import std/tables
+type NoCopies = object
+
+proc `=copy`(a: var NoCopies, b: NoCopies) {.error.}
+
+# bug #24720
+proc foo() =
+  var t: Table[int, NoCopies]
+  t[3] = NoCopies() # only moves
+  for k, v in t.pairs(): # lent values, no need to copy!
+    echo "found entry"
+
+foo()