Allow slice to be whole Vector and then avoid copies for builder.

distribution/lib/Standard/Base/0.0.0-dev/src/Data/Vector.enso

@@ -1085,10 +1085,10 @@ type Builder
                 bldr.to_vector
     to_vector : Vector Any
     to_vector self =
-        ## This creates a fresh copy of the builders storage, so any future
-           changes to the builder will not affect the returned vector.
-        new_array = self.java_builder.toArray
-        from_polyglot_array new_array
+        ## The slice means that if the builder is appended to later, the
+           returned vector remains unchanged.
+        list = self.java_builder.asList
+        from_polyglot_array list . slice 0 list.size
 
 ## UNSTABLE
 

engine/runtime/src/main/java/org/enso/interpreter/runtime/data/Vector.java

@@ -76,10 +76,6 @@ public final Vector slice(long start, long end, InteropLibrary interop)
       return new Vector(new Array(0));
     }
 
-    if ((slice_start == 0) && (slice_end == this_length)) {
-      return this;
-    }
-
     return new Vector(new ArraySlice(this.storage, slice_start, slice_end));
   }
 

std-bits/base/src/main/java/org/enso/base/Array_Builder.java

@@ -50,8 +50,6 @@ public void appendTo(List<T> list) {
     builder.addAll(list);
   }
 
-  /** Converts current content to a new array. */
-  public Object[] toArray() {
-    return builder.toArray();
-  }
+  /** Gets the backing store of the Builder as a List */
+  public List<T> asList() { return builder; }
 }