# Promising Future A glimpse of a promising future in which Ruby supports lazy evaluation.

## Overview

Promises and futures][

both transparently defer the execution of a block.

Promises evaluate the given block if and when its result is first needed. Futures evaluate the given block optimistically in another thread.

require 'promise'
require 'future'    # you can just require 'future' if using both

x = promise { 1 + 2 }
y = future  { sleep 10 && 6 * 7 }

puts x      #=> 3
sleep 5     # ... do work for 5 seconds ...
puts y      #=> 42, after blocking 5 seconds

Note that this is pretty useless in Ruby's interactive shell `irb`, as it will eagerly evaluate everything as part of its read-eval-print loop, forcing promises and futures to yield their results.

The library has been tested with Ruby 1.8.7, 1.9.1 and JRuby 1.5.0. YARD documentation is available at <promise.rubyforge.org/>

## Classes

* {Promise}
* {Future}

## Installation The library is distributed via [RubyGems](rubygems.org/):

$ gem install promise

## Source The source is available at <github.com/bhuga/promising-future>

## Author [Ben Lavender](github.com/bhuga)

## Unlicense Promising Future is free and unencumbered public domain software. For more information, see <unlicense.org/> or the accompanying UNLICENSE file.

[Promises and futures]: en.wikipedia.org/wiki/Futures_and_promises