On 05/19/2017 02:55 PM, Biotronic wrote:
On Friday, 19 May 2017 at 12:21:10 UTC, biocyberman wrote:
1. Why do we need to use assumeUnique in 'revComp0' and 'revComp3'?
D strings are immutable, so if I'd created the result array as a string,
I couldn't change the individual characters. Instead, I create a mutable
array, change the elements in it, then cast it to immutable when I'm
done. assumeUnique does that casting while keeping other type
information and arguably providing better documentation through its
name. Behind the scenes, it's basically doing cast(string)result;
You could alternatively use `.reserve` on a `string`:
----
string result;
result.reserve(N);
for (...) {
result ~= ...;
}
----
That performs worse, though. Probably still has to check every time if
there's reserved space available. On the plus side, it would be `@safe`.
2. What is going on with the trick of making chars enum like that in
'revComp3'?
By marking a symbol enum, we tell the compiler that its value should be
calculated at compile-time. It's a bit of an optimization (but probably
doesn't matter at all, and should be done by the compiler anyway), and a
way to say it's really, really const. :p
You fell into a trap there. The value is calculated at compile time, but
it has copy/paste-like behavior. That is, whenever you use `chars`, the
code behaves as if you typed out the array literal. That means, the
whole array is re-created on every iteration.
Use `static immutable` instead. It still forces compile-time
calculation, but it doesn't have copy/paste behavior. Speeds up revComp3
a lot.
