<i>&gt; Not importing the entire library will result in faster compilation. Unless rust has a concept similar to precompiled headers, etc. I apologize at this point. I&#x27;m not sure what Rust does in that respect, but my initial thoughts were that as the project grows, the parser will slow on includes. The internal symbol resolver will slow on lookups because too many things are included.</i><p>The compilation time problems associated with headers are problems with headers: avoiding headers makes it easy to avoid the problems. The crate system of Rust is somewhat similar to precompiled headers, and C++ is in fact in the process of putting something similar (modules) into the standard.<p>Interestingly, this makes the Rust compiler easier to work with: the basic things of lexing, parsing, name resolution etc. are not at all bottlenecks (any particular file is only parsed once, there&#x27;s not megabytes and megabytes of headers to parse for every invocation). This means these parts don&#x27;t have to be micro-optimised, and hence don&#x27;t get hit by an increase in complexity due to those optimisations.<p>Concerns about internal symbol resolution aren&#x27;t a problem: hashmaps give (expected) O(1) access no matter how many elements they hold, and even using a tree has O(log n) access (i.e. going from 1_000 symbols to 1_000_000 only doubles the time for a look-up, and the next doubling happens at 1_000_000_000_000 symbols).<p><i>&gt; Since both are supported, maybe the parser can be made smarter?</i><p>Not sure what this has got to do with the parser (7..0 <i>parses</i> fine, it just creates an empty iterator), but implicitly reversing ranges are on of the most annoying features of R: it makes it annoyingly hard to do things like `x..y - 3`.<p><i>&gt;  Well this piece of code:</i><p>Two things: the author is effectively golfing here (they say they want the code to fit on a single page), and, the Rust version can be written just like the C++ version, with a loop:<p><pre><code>  let scores = [counts[count]; 7];
  for &amp;word in words {
      if word &amp; !seven == 0 {
          for place in 0..7 {
              scores[place] += (word &gt;&gt; bits[places]) &amp; 1;
          }
      }
  }</code></pre>