Add string comparison operator overloads (#64)

std/assembly/string.ts

@@ -127,6 +127,91 @@ export class String {
     );
   }
 
+  @operator("!=")
+  private static __ne(left: String, right: String): bool {
+    return !this.__eq(left, right);
+  }
+
+  @operator(">")
+  private static __gt(left: String, right: String): bool {
+    if (!changetype<usize>(left) || !changetype<usize>(right)) {
+      return false;
+    }
+
+    var leftLength  = left.length;
+    var rightLength = right.length;
+
+    if (!leftLength)  return false;
+    if (!rightLength) return true;
+
+    var length = <usize>min<i32>(leftLength, rightLength);
+    return compare_memory(
+      changetype<usize>(left)  + HEADER_SIZE,
+      changetype<usize>(right) + HEADER_SIZE,
+      length << 1
+    ) > 0;
+  }
+
+  @operator(">=")
+  private static __gte(left: String, right: String): bool {
+    if (!changetype<usize>(left) || !changetype<usize>(right)) {
+      return false;
+    }
+
+    var leftLength  = left.length;
+    var rightLength = right.length;
+
+    if (!leftLength)  return !rightLength;
+    if (!rightLength) return true;
+
+    var length = <usize>min<i32>(leftLength, rightLength);
+    return compare_memory(
+      changetype<usize>(left)  + HEADER_SIZE,
+      changetype<usize>(right) + HEADER_SIZE,
+      length << 1
+    ) >= 0;
+  }
+
+  @operator("<")
+  private static __lt(left: String, right: String): bool {
+    if (!changetype<usize>(left) || !changetype<usize>(right)) {
+      return false;
+    }
+
+    var leftLength  = left.length;
+    var rightLength = right.length;
+
+    if (!rightLength) return false;
+    if (!leftLength)  return true;
+
+    var length = <usize>min<i32>(leftLength, rightLength);
+    return compare_memory(
+      changetype<usize>(left)  + HEADER_SIZE,
+      changetype<usize>(right) + HEADER_SIZE,
+      length << 1
+    ) < 0;
+  }
+
+  @operator("<=")
+  private static __lte(left: String, right: String): bool {
+    if (!changetype<usize>(left) || !changetype<usize>(right)) {
+      return false;
+    }
+
+    var leftLength  = left.length;
+    var rightLength = right.length;
+
+    if (!rightLength) return !leftLength;
+    if (!leftLength)  return true;
+
+    var length = <usize>min<i32>(leftLength, rightLength);
+    return compare_memory(
+      changetype<usize>(left)  + HEADER_SIZE,
+      changetype<usize>(right) + HEADER_SIZE,
+      length << 1
+    ) <= 0;
+  }
+
   includes(searchString: String, position: i32 = 0): bool {
     return this.indexOf(searchString, position) != -1;
   }

tests/compiler/std/string.ts

@@ -3,6 +3,7 @@ import "allocator/arena";
 // preliminary
 
 var str: string = "hi, I'm a string";
+var nullStr: String;
 
 // exactly once in static memory
 assert(changetype<usize>(str) == changetype<usize>("hi, I'm a string"));
@@ -36,3 +37,26 @@ assert(parseFloat(".1foobar") == 0.1);
 
 var c = "a" + "b";
 assert(c == "ab");
+assert(c != "a");
+assert("" == "");
+assert("" != nullStr);
+
+assert("b" > "a");
+assert("ba" > "a");
+assert("ba" >= "aa");
+assert("ba" > "ab");
+assert(!("ba" < "ab"));
+
+assert(!("b" < nullStr));
+assert(!(nullStr < "b"));
+
+assert("abc" > "");
+assert("" < "abc");
+assert("abc" >= "");
+assert("" <= "abc");
+assert(!("abc" < ""));
+assert(!("" > "abc"));
+assert(!("" < ""));
+assert(!("" > ""));
+assert("" >= "");
+assert("" <= "");