Question

I thought I’d throw out this problem to see what elegant solutions folk
could come up with and, in the process, hopefully learn some new ruby
tricks.

I’ll set the problem in the context of producing a twitter message,
which has a maximum length of 140 characters. I’m looking for a concise
function that will deliver a tweet no longer than 140 characters from
three inputs: text_a (mandatory), text_b (optional), boolean that
triggers a function that returns a string (optional).

(I’ve used the twitter-text gem to take byte, char, and encoding issues
out of play, as that is not the focus of the problem.)

The main constraint is that to achieve the required maximum length, it
is text_a that must be truncated.

Here’s some long-winded sample code (working, I think) that hopefully
makes the requirement clear.

# encoding: utf-8

require 'twitter-text'

def tweet(text_a, text_b=nil, suffix=false)
  text = "fixed preamble #{text_a}"
  text << " #{text_b}" if text_b
  text << get_suffix if suffix
  return text unless Twitter::Validation.tweet_invalid?(text) == :too_long
  excess_length = Twitter::Validation.tweet_length(text) - Twitter::Validation::MAX_LENGTH
  text_a = text_a[0..-(excess_length + 1)]
  text = "fixed preamble #{text_a}"
  text << " #{text_b}" if text_b
  text << get_suffix if suffix
  text
end

def get_suffix
  " some generated suffix"
end

It’s ugly, especially with the duplication. Ideas?

Answer 1

Why not build the string properly in the first place?

def tweet(text_a, text_b=nil, suffix=false)
  text = ""
  text << " #{text_b}" if text_b
  text << get_suffix if suffix

  space = Twitter::Validation::MAX_LENGTH - Twitter::Validation.tweet_length(text)
  raise "too long" unless space > 0

  "fixed preamble #{text_a}"[0, space] + text
end