reworked emit pragma; fixes #4730

tests/cpp/temitlist.nim

@@ -0,0 +1,22 @@
+discard """
+  cmd: "nim cpp $file"
+  output: '''6.0'''
+"""
+
+# bug #4730
+
+type Vector* {.importcpp: "std::vector", header: "<vector>".}[T] = object
+
+template `[]=`*[T](v: var Vector[T], key: int, val: T) =
+  {.emit: [v, "[", key, "] = ", val, ";"].}
+
+proc setLen*[T](v: var Vector[T]; size: int) {.importcpp: "resize", nodecl.}
+proc `[]`*[T](v: var Vector[T], key: int): T {.importcpp: "(#[#])", nodecl.}
+
+proc main =
+  var v: Vector[float]
+  v.setLen 1
+  v[0] = 6.0
+  echo v[0]
+
+main()