1 files changed, 97 insertions, 0 deletions
diff --git a/tests/destructor/tcustomstrings.nim b/tests/destructor/tcustomstrings.nim
new file mode 100644
index 000000000..afd2fa838
--- /dev/null
+++ b/tests/destructor/tcustomstrings.nim
@@ -0,0 +1,97 @@
+discard """
+  output: '''foo bar to appendmore here
+foo bar to appendmore here
+foo bar to appendmore here
+foo bar to appendmore here
+foo bar to appendmore here
+after 16 16'''
+  cmd: '''nim c --newruntime $file'''
+"""
+
+type
+  mystring = object
+    len, cap: int
+    data: ptr UncheckedArray[char]
+
+{.this: self.}
+
+var
+  allocCount, deallocCount: int
+
+proc `=destroy`*(self: var mystring) =
+  if data != nil:
+    dealloc(data)
+    inc deallocCount
+    data = nil
+    len = 0
+    cap = 0
+
+proc `=sink`*(a: var mystring, b: mystring) =
+  # we hope this is optimized away for not yet alive objects:
+  if a.data != nil and a.data != b.data:
+    dealloc(a.data)
+    inc deallocCount
+  a.len = b.len
+  a.cap = b.cap
+  a.data = b.data
+
+proc `=`*(a: var mystring; b: mystring) =
+  if a.data != nil and a.data != b.data:
+    dealloc(a.data)
+    inc deallocCount
+    a.data = nil
+  a.len = b.len
+  a.cap = b.cap
+  if b.data != nil:
+    a.data = cast[type(a.data)](alloc(a.cap + 1))
+    inc allocCount
+    copyMem(a.data, b.data, a.cap+1)
+
+proc resize(self: var mystring) =
+  if cap == 0: cap = 8
+  else: cap = (cap * 3) shr 1
+  if data == nil: inc allocCount
+  data = cast[type(data)](realloc(data, cap + 1))
+
+proc add*(self: var mystring; c: char) =
+  if self.len >= self.cap: resize(self)
+  self.data[self.len] = c
+  self.data[self.len+1] = '\0'
+  inc self.len
+
+proc ensure(self: var mystring; newLen: int) =
+  if newLen >= cap:
+    cap = max((cap * 3) shr 1, newLen)
+    if cap > 0:
+      if data == nil: inc allocCount
+      data = cast[type(data)](realloc(data, cap + 1))
+
+proc add*(self: var mystring; y: mystring) =
+  let newLen = len + y.len
+  ensure(self, newLen)
+  copyMem(addr data[len], y.data, y.data.len + 1)
+  len = newLen
+
+proc create*(lit: string): mystring =
+  let newLen = lit.len
+  ensure(result, newLen)
+  copyMem(addr result.data[result.len], unsafeAddr lit[0], newLen + 1)
+  result.len = newLen
+
+func `&`*(a, b: mystring): mystring =
+  result = a
+  result.add b
+
+func main(n: int) =
+  var a: mystring
+  let b = create" to append"
+  for i in 0..<n:
+    if i > 4: break
+    a = create"foo bar"
+    let c = b & create"more here"
+    a.add c
+    echo cstring(a.data)
+
+
+main(1000)
+echo "after ", allocCount, " ", deallocCount