Time for an 2014 update…

Task/Run-length-encoding/D/run-length-encoding-2.d

@@ -1,29 +1,30 @@
 import std.stdio, std.array, std.conv;
 
 // Similar to the 'look and say' function.
-string encode(in string input) {
-    if (input.empty) return input;
+string encode(in string input) pure /*nothrow*/ {
+    if (input.empty)
+        return input;
     char last = input[$ - 1];
     string output;
     int count;
 
-    foreach_reverse (c; input) {
+    foreach_reverse (immutable c; input) {
         if (c == last) {
             count++;
         } else {
-            output = text(count) ~ last ~ output;
+            output = count.text ~ last ~ output;
             count = 1;
             last = c;
         }
     }
 
-    return text(count) ~ last ~ output;
+    return count.text ~ last ~ output;
 }
 
-string decode(in string input) {
+string decode(in string input) pure {
     string i, result;
 
-    foreach (c; input)
+    foreach (immutable c; input)
         switch (c) {
             case '0': .. case '9':
                 i ~= c;
@@ -32,12 +33,11 @@ string decode(in string input) {
                 if (i.empty)
                     throw new Exception("Can not repeat a letter " ~
                         "without a number of repetitions");
-                result ~= replicate([c], to!int(i));
+                result ~= [c].replicate(i.to!int);
                 i.length = 0;
                 break;
             default:
-                throw new Exception("'" ~ c ~
-                                    "' is not alphanumeric");
+                throw new Exception("'" ~ c ~ "' is not alphanumeric");
         }
 
     return result;
@@ -47,7 +47,7 @@ void main() {
     immutable txt = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWW" ~
                     "WWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
     writeln("Input: ", txt);
-    immutable encoded = encode(txt);
+    immutable encoded = txt.encode;
     writeln("Encoded: ", encoded);
-    assert(txt == decode(encoded));
+    assert(txt == encoded.decode);
 }