std/with support field assign (#14484)

* std/with support filed assign

* add changelog

* add support x.dup.with

* add example

* revert support x.dup.with; add example

* update changelog; fix assignment in parameter

* Update changelog.md

* add example for assignment in parameter

* Remove colon style assign

Co-authored-by: Clyybber <darkmine956@gmail.com>

lib/std/with.nim

@@ -41,6 +41,7 @@ when isMainModule:
   type
     Foo = object
       col, pos: string
+      name: string
 
   proc setColor(f: var Foo; r, g, b: int) = f.col = $(r, g, b)
   proc setPosition(f: var Foo; x, y: float) = f.pos = $(x, y)
@@ -49,3 +50,9 @@ when isMainModule:
   with(f, setColor(2, 3, 4), setPosition(0.0, 1.0))
   echo f
 
+  f = Foo()
+  with f:
+    col = $(2, 3, 4)
+    pos = $(0.0, 1.0)
+    _.name = "bar"
+  echo f