Coder in the sky with diamonds

thoughts on code and tech

Ruby sniplets for optimized tasks

28 Jun 2016

Reading a file

enum = file.lines
100.times{enum.next} # offset 100 lines
enum.take(100) # take the next 100

Reading from socket

require "socket"
server = TCPServer.open(8080)
loop do
    Thread.fork(server.accept) do |client| 
        reply = "Connected!"
        client.puts(reply)
        client.close
    end
end

The loop directive is more terse than while true

Dynamic dispatch

This is my solution to the coderbyte’s Reverse polish notation challenge. It illustrates ruby’s send method dispatch

  expression = "+ - 1 2 5"
  operands = []
  evaluated = []
  
  expression.each do |c|
    case c 
    	when /\d/
      		evaluated.push(c.to_f)
        when "-", "/", "*", "+", "**"
      		operands = evaluated.pop(2)
      		evaluated.push(operands.first.send(c, operands[1]))
    end 
  end  
  evaluated.first.to_i

Rails gotcha, avoid active record magic when dealing with bulk objects

Consider you are trying to recover all tags, you’re inclined to write:

tasks = Task.find(:all, :include => :tags)

But tags are often value objects, only their name matters and there’s often no logic attached to this state. So consider using instead:

tags = Tag.select <<-MLINE
      *,
      array(
        select tags.name from tags inner join product_tags on (tags.id = products_tags.tag_id)
        where products_tags.product_id=products.id
      ) as tag_names
    MLINE

It’s much less sexy but much faster.

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