From 9acfc43119d42d7265497fd6ae60eda3903d9938 Mon Sep 17 00:00:00 2001
From: Zahary Karadjov <zahary@gmail.comy>
Date: Sun, 11 Sep 2011 21:43:12 +0300
Subject: using statement (ala C#) implemented as macro (added as test).

simplified the usage of the interpolatedFragments iterator.
---
 tests/accept/run/tusingstatement.nim | 102 +++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 tests/accept/run/tusingstatement.nim

(limited to 'tests/accept/run/tusingstatement.nim')

diff --git a/tests/accept/run/tusingstatement.nim b/tests/accept/run/tusingstatement.nim
new file mode 100644
index 000000000..0017af556
--- /dev/null
+++ b/tests/accept/run/tusingstatement.nim
@@ -0,0 +1,102 @@
+discard """
+  file: "tusingstatement.nim"
+  output: "Using test.Closing test."
+"""
+
+import 
+  macros
+
+# This macro mimics the using statement from C#
+#
+# XXX: 
+#  It doen't match the C# version exactly yet.
+#  In particular, it's not recursive, which prevents it from dealing 
+#  with exceptions thrown from the variable initializers when multiple.
+#  variables are used.
+#
+#  Also, since nimrod relies less on exceptions in general, a more
+#  idiomatic definition could be:
+#  var x = init()
+#  if opened(x): 
+#    try:
+#      body
+#    finally:
+#      close(x)
+#
+#  `opened` here could be an overloaded proc which any type can define.
+#  A common practice can be returing an Optional[Resource] obj for which
+#  `opened` is defined to `optional.hasValue`
+macro using(e: expr) : stmt =
+  if e.len != 2:
+    error "Using statement: unexpected number of arguments. Got " &
+      $e.len & ", expected: 1 or more variable assignments and a block"
+
+  var args = e[0]
+  var body = e[1]
+  
+  var 
+    variables : seq[PNimrodNode]
+    closingCalls : seq[PNimrodNode]
+
+  newSeq(variables, 0)
+  newSeq(closingCalls, 0)
+
+  for i in countup(1, args.len-1):
+    if args[i].kind == nnkExprEqExpr:
+      var varName = args[i][0]
+      var varValue = args[i][1]
+ 
+      var varAssignment = newNimNode(nnkIdentDefs)
+      varAssignment.add(varName)
+      varAssignment.add(newNimNode(nnkEmpty)) # empty means no type
+      varAssignment.add(varValue)
+      variables.add(varAssignment)
+
+      closingCalls.add(newCall(!"close", varName))
+    else:
+      error "Using statement: Unexpected expression. Got " &
+        $args[i].kind & " instead of assignment."
+  
+  var varSection = newNimNode(nnkVarSection)
+  varSection.add(variables)
+
+  var finallyBlock = newNimNode(nnkStmtList)
+  finallyBlock.add(closingCalls)
+
+  # XXX: Use a template here once getAst is working properly
+  var targetAst = parseStmt"""block:
+    var
+      x = foo()
+      y = bar()
+
+    try:
+      body()
+
+    finally:
+      close x
+      close y
+  """
+
+  targetAst[0][1][0] = varSection
+  targetAst[0][1][1][0] = body
+  targetAst[0][1][1][1][0] = finallyBlock
+  
+  return targetAst
+
+type 
+  TResource* = object
+    field*: string
+
+proc openResource(param: string): TResource =
+  result.field = param
+
+proc close(r: var TResource) =
+  write(stdout, "Closing " & r.field & ".")
+
+proc use(r: var TResource) =
+  write(stdout, "Using " & r.field & ".")
+
+using(r = openResource("test")):
+  use r
+
+
-- 
cgit 1.4.1-2-gfad0