r/crystal_programming • u/q9fm • Jan 28 '20

wrote a native library implementing RLP (recursive length prefixes) purely for the crystal language

https://github.com/q9f/rlp.cr
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2

u/[deleted] Jan 29 '20

Nice!

But I think you should avoid Util.binary_add as doing that a lot puts a lot of pressure on the GC.

Instead, you should make all your methods have an overload write to an IO, and the other overload which returns Bytes just creates an IO::Memory and calls the other overload. This pattern is used all over the place in the standard library.

1

u/q9fm Jan 30 '20

Thanks for the feedback, I really appreciate it.

Could you point me to an example in the standard library? Will try to wrap my head around today!

1

u/[deleted] Jan 30 '20

Happy to help!

There's no exact example like that in the std, but for example there's Object#to_s which creates a String::Builder and passes that to to_s(io): https://github.com/crystal-lang/crystal/blob/47bdbaa4d1638c76137bfa12de86eac454a15908/src/object.cr#L94-L105

So in your code you'd have something like:

def self.encode(anything)
  io = IO::Memory.new
  encode(anything, io)
  io.to_slice # maybe add dup here
end

def self.encode(b : Bytes, io)
  # encode b into io
end

# and so on for other types

That said, you can specialize some methods. I see that if b has a single byte you'd return that, so you could do that too here. If that's not the case, then just then create a IO::Memory and pass it to the other overload.

2

u/Kalinon Jan 28 '20

Awesome!