add overload add(a: var string, b: openArray[char])

changelog.md

@@ -35,6 +35,8 @@
 
 - `doAssertRaises` now correctly handles foreign exceptions.
 
+- Added overload `ssytem.add(a: var string, b: openArray[char])`
+
 ## Language changes
 
 - `nimscript` now handles `except Exception as e`

lib/system.nim

@@ -1032,6 +1032,18 @@ proc add*(x: var string, y: string) {.magic: "AppendStrStr", noSideEffect.}
   ##   tmp.add("cd")
   ##   assert(tmp == "abcd")
 
+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.
+  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
 
 type
   Endianness* = enum ## Type describing the endianness of a processor.

tests/vm/tstring_openarray.nim

@@ -13,6 +13,7 @@ proc set_all[T](s: var openArray[T]; val: T) =
     s[i] = val
 
 proc test() =
+  block:
     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]
@@ -22,6 +23,18 @@ proc test() =
     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]
+  block:
+    var a0 = "hi"
+    var b0 = "foobar"
+    when nimvm:
+      discard # otherwise hits: 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'
 
 const constval0 = "hello".map(proc(x: char): char = x)
 const constval1 = [1,2,3,4].map(proc(x: int): int = x)
@@ -31,4 +44,4 @@ doAssert([1,2,3,4].map(proc(x: int): int = x) == constval1)
 
 test()
 static:
-    test()
+  test()