diff --git a/changelog.md b/changelog.md
index db5b3c14b4d79..aff858818561e 100644
--- a/changelog.md
+++ b/changelog.md
@@ -173,9 +173,10 @@ provided by the operating system.
   dumping (on select signals) and notifying the parent process about the cause
   of termination.
 
-- `hashes.hash` now supports `object`, but can be overloaded.
+- Added `std/strbasics` for high performance string operations.
+  Added `strip`, `setSlice`, `add(a: var string, b: openArray[char])`.
 
-- Added `strip` and `setSlice` to `std/strbasics`.
+- `hashes.hash` now supports `object`, but can be overloaded.
 
 - Added to `wrapnils` an option-like API via `??.`, `isSome`, `get`.
 
diff --git a/lib/std/strbasics.nim b/lib/std/strbasics.nim
index ce061adca59ac..357e562084a85 100644
--- a/lib/std/strbasics.nim
+++ b/lib/std/strbasics.nim
@@ -8,9 +8,25 @@
 #
 
 ## This module provides some high performance string operations.
+##
+## Experimental API, subject to change.
 
 const whitespaces = {' ', '\t', '\v', '\r', '\l', '\f'}
 
+proc add*(x: var string, y: openArray[char]) =
+  ## Concatenates `x` and `y` in place. `y` must not overlap with `x` to
+  ## allow future `memcpy` optimizations.
+  # Use `{.noalias.}` ?
+  let n = x.len
+  x.setLen n + y.len
+    # pending https://github.com/nim-lang/Nim/issues/14655#issuecomment-643671397
+    # use x.setLen(n + y.len, isInit = false)
+  var i = 0
+  while i < y.len:
+    x[n + i] = y[i]
+    i.inc
+  # xxx use `nimCopyMem(x[n].addr, y[0].addr, y.len)` after some refactoring
+
 func stripSlice(s: openArray[char], leading = true, trailing = true, chars: set[char] = whitespaces): Slice[int] =
   ## Returns the slice range of `s` which is stripped `chars`.
   runnableExamples:
diff --git a/lib/system.nim b/lib/system.nim
index 6d26beb73f0ed..4b182905b7313 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -1069,15 +1069,16 @@ proc add*(x: var string, y: char) {.magic: "AppendStrCh", noSideEffect.}
   ##   tmp.add('a')
   ##   tmp.add('b')
   ##   assert(tmp == "ab")
-proc add*(x: var string, y: string) {.magic: "AppendStrStr", noSideEffect.}
+
+proc add*(x: var string, y: string) {.magic: "AppendStrStr", noSideEffect.} =
   ## Concatenates `x` and `y` in place.
   ##
-  ## .. code-block:: Nim
-  ##   var tmp = ""
-  ##   tmp.add("ab")
-  ##   tmp.add("cd")
-  ##   assert(tmp == "abcd")
-
+  ## See also `strbasics.add`.
+  runnableExamples:
+    var tmp = ""
+    tmp.add("ab")
+    tmp.add("cd")
+    assert tmp == "abcd"
 
 type
   Endianness* = enum ## Type describing the endianness of a processor.
diff --git a/tests/stdlib/tstrbasics.nim b/tests/stdlib/tstrbasics.nim
index 4dd232351ecbd..8a3b22889db9c 100644
--- a/tests/stdlib/tstrbasics.nim
+++ b/tests/stdlib/tstrbasics.nim
@@ -1,126 +1,139 @@
 discard """
   targets: "c cpp js"
+  matrix: "--gc:refc; --gc:arc"
 """
 
 import std/[strbasics, sugar]
 
-
-proc teststrip() =
-  var a = "  vhellov   "
-  strip(a)
-  doAssert a == "vhellov"
-
-  a = "  vhellov   "
-  a.strip(leading = false)
-  doAssert a == "  vhellov"
-
-  a = "  vhellov   "
-  a.strip(trailing = false)
-  doAssert a == "vhellov   "
-
-  a.strip()
-  a.strip(chars = {'v'})
-  doAssert a == "hello"
-
-  a = "  vhellov   "
-  a.strip()
-  a.strip(leading = false, chars = {'v'})
-  doAssert a == "vhello"
-
-  var c = "blaXbla"
-  c.strip(chars = {'b', 'a'})
-  doAssert c == "laXbl"
-  c = "blaXbla"
-  c.strip(chars = {'b', 'a', 'l'})
-  doAssert c == "X"
-
-  block:
-    var a = "xxxxxx"
-    a.strip(chars={'x'})
-    doAssert a.len == 0
-
-  block:
-    var a = "x"
-    a.strip(chars={'x'})
-    doAssert a.len == 0
-  
-  block:
-    var a = "x"
-    a.strip(chars={'1'})
-    doAssert a.len == 1
-
-  block:
-    var a = ""
-    a.strip(chars={'x'})
-    doAssert a.len == 0
-
-  block:
-    var a = "xxx xxx"
-    a.strip(chars={'x'})
-    doAssert a == " "
-
-  block:
-    var a = "xxx  wind"
-    a.strip(chars={'x'})
-    doAssert a == "  wind"
-
-  block:
-    var a = "xxx  iii"
-    a.strip(chars={'i'})
-    doAssert a == "xxx  "
-
-  block:
-    var a = "xxx  iii"
-    doAssert a.dup(strip(chars = {'i'})) == "xxx  "
-    doAssert a.dup(strip(chars = {' '})) == "xxx  iii"
-    doAssert a.dup(strip(chars = {'x'})) == "  iii"
-    doAssert a.dup(strip(chars = {'x', ' '})) == "iii"
-    doAssert a.dup(strip(chars = {'x', 'i'})) == "  "
-    doAssert a.dup(strip(chars = {'x', 'i', ' '})).len == 0
-
-  block:
-    var a = "x  i"
-    doAssert a.dup(strip(chars = {'i'})) == "x  "
-    doAssert a.dup(strip(chars = {' '})) == "x  i"
-    doAssert a.dup(strip(chars = {'x'})) == "  i"
-    doAssert a.dup(strip(chars = {'x', ' '})) == "i"
-    doAssert a.dup(strip(chars = {'x', 'i'})) == "  "
-    doAssert a.dup(strip(chars = {'x', 'i', ' '})).len == 0
-
-  block:
-    var a = ""
-    doAssert a.dup(strip(chars = {'i'})).len == 0
-    doAssert a.dup(strip(chars = {' '})).len == 0
-    doAssert a.dup(strip(chars = {'x'})).len == 0
-    doAssert a.dup(strip(chars = {'x', ' '})).len == 0
-    doAssert a.dup(strip(chars = {'x', 'i'})).len == 0
-    doAssert a.dup(strip(chars = {'x', 'i', ' '})).len == 0
-
-  block:
-    var a = " "
-    doAssert a.dup(strip(chars = {'i'})) == " "
-    doAssert a.dup(strip(chars = {' '})).len == 0
-    doAssert a.dup(strip(chars = {'x'})) == " "
-    doAssert a.dup(strip(chars = {'x', ' '})).len == 0
-    doAssert a.dup(strip(chars = {'x', 'i'})) == " "
-    doAssert a.dup(strip(chars = {'x', 'i', ' '})).len == 0
-
-
-  block:
-    var a = "Hello, Nim!"
-    doassert a.dup(setSlice(7 .. 9)) == "Nim"
-    doAssert a.dup(setSlice(0 .. 0)) == "H"
-    doAssert a.dup(setSlice(0 .. 1)) == "He"
-    doAssert a.dup(setSlice(0 .. 10)) == a
-    doAssert a.dup(setSlice(1 .. 0)).len == 0
-    doAssert a.dup(setSlice(20 .. -1)).len == 0
-
-
-    doAssertRaises(AssertionDefect):
-      discard a.dup(setSlice(-1 .. 1))
-
-    doAssertRaises(AssertionDefect):
-      discard a.dup(setSlice(1 .. 11))
-
-static: teststrip()
-teststrip()
+proc main() =
+  when not defined(gcArc): # pending bug #17173
+    block: # strip
+      var a = "  vhellov   "
+      strip(a)
+      doAssert a == "vhellov"
+
+      a = "  vhellov   "
+      a.strip(leading = false)
+      doAssert a == "  vhellov"
+
+      a = "  vhellov   "
+      a.strip(trailing = false)
+      doAssert a == "vhellov   "
+
+      a.strip()
+      a.strip(chars = {'v'})
+      doAssert a == "hello"
+
+      a = "  vhellov   "
+      a.strip()
+      a.strip(leading = false, chars = {'v'})
+      doAssert a == "vhello"
+
+      var c = "blaXbla"
+      c.strip(chars = {'b', 'a'})
+      doAssert c == "laXbl"
+      c = "blaXbla"
+      c.strip(chars = {'b', 'a', 'l'})
+      doAssert c == "X"
+
+      block:
+        var a = "xxxxxx"
+        a.strip(chars={'x'})
+        doAssert a.len == 0
+
+      block:
+        var a = "x"
+        a.strip(chars={'x'})
+        doAssert a.len == 0
+      
+      block:
+        var a = "x"
+        a.strip(chars={'1'})
+        doAssert a.len == 1
+
+      block:
+        var a = ""
+        a.strip(chars={'x'})
+        doAssert a.len == 0
+
+      block:
+        var a = "xxx xxx"
+        a.strip(chars={'x'})
+        doAssert a == " "
+
+      block:
+        var a = "xxx  wind"
+        a.strip(chars={'x'})
+        doAssert a == "  wind"
+
+      block:
+        var a = "xxx  iii"
+        a.strip(chars={'i'})
+        doAssert a == "xxx  "
+
+      block:
+        var a = "xxx  iii"
+        doAssert a.dup(strip(chars = {'i'})) == "xxx  "
+        doAssert a.dup(strip(chars = {' '})) == "xxx  iii"
+        doAssert a.dup(strip(chars = {'x'})) == "  iii"
+        doAssert a.dup(strip(chars = {'x', ' '})) == "iii"
+        doAssert a.dup(strip(chars = {'x', 'i'})) == "  "
+        doAssert a.dup(strip(chars = {'x', 'i', ' '})).len == 0
+
+      block:
+        var a = "x  i"
+        doAssert a.dup(strip(chars = {'i'})) == "x  "
+        doAssert a.dup(strip(chars = {' '})) == "x  i"
+        doAssert a.dup(strip(chars = {'x'})) == "  i"
+        doAssert a.dup(strip(chars = {'x', ' '})) == "i"
+        doAssert a.dup(strip(chars = {'x', 'i'})) == "  "
+        doAssert a.dup(strip(chars = {'x', 'i', ' '})).len == 0
+
+      block:
+        var a = ""
+        doAssert a.dup(strip(chars = {'i'})).len == 0
+        doAssert a.dup(strip(chars = {' '})).len == 0
+        doAssert a.dup(strip(chars = {'x'})).len == 0
+        doAssert a.dup(strip(chars = {'x', ' '})).len == 0
+        doAssert a.dup(strip(chars = {'x', 'i'})).len == 0
+        doAssert a.dup(strip(chars = {'x', 'i', ' '})).len == 0
+
+      block:
+        var a = " "
+        doAssert a.dup(strip(chars = {'i'})) == " "
+        doAssert a.dup(strip(chars = {' '})).len == 0
+        doAssert a.dup(strip(chars = {'x'})) == " "
+        doAssert a.dup(strip(chars = {'x', ' '})).len == 0
+        doAssert a.dup(strip(chars = {'x', 'i'})) == " "
+        doAssert a.dup(strip(chars = {'x', 'i', ' '})).len == 0
+
+    block: # setSlice
+      var a = "Hello, Nim!"
+      doassert a.dup(setSlice(7 .. 9)) == "Nim"
+      doAssert a.dup(setSlice(0 .. 0)) == "H"
+      doAssert a.dup(setSlice(0 .. 1)) == "He"
+      doAssert a.dup(setSlice(0 .. 10)) == a
+      doAssert a.dup(setSlice(1 .. 0)).len == 0
+      doAssert a.dup(setSlice(20 .. -1)).len == 0
+
+      doAssertRaises(AssertionDefect):
+        discard a.dup(setSlice(-1 .. 1))
+
+      doAssertRaises(AssertionDefect):
+        discard a.dup(setSlice(1 .. 11))
+
+  block: # add
+    var a0 = "hi"
+    var b0 = "foobar"
+    when nimvm:
+      discard # pending bug #15952
+    else:
+      a0.add b0.toOpenArray(1,3)
+      doAssert a0 == "hioob"
+    proc fn(c: openArray[char]): string =
+      result.add c
+    doAssert fn("def") == "def"
+    doAssert fn(['d','\0', 'f'])[2] == 'f'
+
+static: main()
+main()
diff --git a/tests/vm/tstring_openarray.nim b/tests/vm/tstring_openarray.nim
index 1b8a1304c9cc2..9318344f85292 100644
--- a/tests/vm/tstring_openarray.nim
+++ b/tests/vm/tstring_openarray.nim
@@ -12,16 +12,16 @@ proc set_all[T](s: var openArray[T]; val: T) =
   for i in 0..<s.len:
     s[i] = val
 
-proc test() =
-    var a0 = "hello_world"
-    var a1 = [1,2,3,4,5,6,7,8,9]
-    var a2 = @[1,2,3,4,5,6,7,8,9]
-    a0.set_all('i')
-    a1.set_all(4)
-    a2.set_all(4)
-    doAssert a0 == "iiiiiiiiiii"
-    doAssert a1 == [4,4,4,4,4,4,4,4,4]
-    doAssert a2 == @[4,4,4,4,4,4,4,4,4]
+proc main() =
+  var a0 = "hello_world"
+  var a1 = [1,2,3,4,5,6,7,8,9]
+  var a2 = @[1,2,3,4,5,6,7,8,9]
+  a0.set_all('i')
+  a1.set_all(4)
+  a2.set_all(4)
+  doAssert a0 == "iiiiiiiiiii"
+  doAssert a1 == [4,4,4,4,4,4,4,4,4]
+  doAssert a2 == @[4,4,4,4,4,4,4,4,4]
 
 const constval0 = "hello".map(proc(x: char): char = x)
 const constval1 = [1,2,3,4].map(proc(x: int): int = x)
@@ -29,6 +29,5 @@ const constval1 = [1,2,3,4].map(proc(x: int): int = x)
 doAssert("hello".map(proc(x: char): char = x) == constval0)
 doAssert([1,2,3,4].map(proc(x: int): int = x) == constval1)
 
-test()
-static:
-    test()
+static: main()
+main()