SIP-11 String Interpolation Simplification

Changed StringContext.f which implements the formatted
string interpolator.

Any '%' not in formatting position is left in the resulting string literally.
However, instead of adding %s format holders and extending the args with "%"
expressions, these '%' are replaced by '%%'. The formatter then converts '%%'
(percent formatter) to the literal '%' (\u0025). This also simplifies the spec.

The interpolation tests still pass.

1 files changed, 12 insertions, 14 deletions

diff --git a/src/library/scala/StringContext.scala b/src/library/scala/StringContext.scala
index 882451680a..06620a82a1 100644
--- a/src/library/scala/StringContext.scala
+++ b/src/library/scala/StringContext.scala
@@ -79,15 +79,13 @@ case class StringContext(parts: String*) {
    *      start a format specifier), then the string format specifier `%s` is inserted.
    *
    *   2. Any `%` characters not in formatting positions are left in the resulting
-   *      string literally. This is achieved by replacing each such occurrence by a string
-   *      format specifier `%s` and adding a corresponding argument string `"%"`.
+   *      string literally. This is achieved by replacing each such occurrence by the string
+   *      format specifier `%%`.
    */
   def f(args: Any*) = {
     checkLengths(args: _*)
     val pi = parts.iterator
-    val ai = args.iterator
     val bldr = new java.lang.StringBuilder
-    val args1 = new ArrayBuffer[Any]
     def copyString(first: Boolean): Unit = {
       val str = treatEscapes(pi.next())
       val strIsEmpty = str.length == 0
@@ -98,23 +96,23 @@ case class StringContext(parts: String*) {
           bldr append "%s"
         idx = 1
       }
-      val len = str.length
-      while (idx < len) {
-        if (str(idx) == '%') {
-          bldr append (str substring (start, idx)) append "%s"
-          args1 += "%"
-          start = idx + 1
+      if (!strIsEmpty) {
+        val len = str.length
+        while (idx < len) {
+          if (str(idx) == '%') {
+            bldr append (str substring (start, idx)) append "%%"
+            start = idx + 1
+          }
+          idx += 1
         }
-        idx += 1
+        bldr append (str substring (start, idx))
       }
-      if (!strIsEmpty) bldr append (str substring (start, idx))
     }
     copyString(first = true)
     while (pi.hasNext) {
-      args1 += ai.next()
       copyString(first = false)
     }
-    bldr.toString format (args1: _*)
+    bldr.toString format (args: _*)
   }
 }