application as data flow - lscc talks #5

Building watertight business logic

Application asdata flow

@tehmou

Functional Reactive Programming» Also known as FRP or Rx

» Streams over variables

» Push over pull

» Pure functions over stateful objects

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Stream is a pub/subWith no events – just data

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Observable Observer

.. with some operations in between.. that can change the type of data

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Observable 1

Observer

filter

combine latest

Observable 2

Example:Github searchSearching repositories by name and minimum number of watchers08/21/14

The API» https://api.github.com/search/repositories?q=xxx

» Open API with an aggressive rate limit

» Should not be hit too often

» JSON response with details about the repo

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Search input» Search only when more than two characters present

» Do not search until the text has been unchanged for 500ms

» Add ability to filter by a minimum watcher count

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Text input Data flowarchitecture

UI Events

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Text input

convert eventsto strings

Data flowarchitecture

String

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Text input

filter/throttle

convert eventsto strings

Data flowarchitecture

String(some are discarded)

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Text input

filter/throttle

API APInetwork

convert eventsto strings

Data flowarchitecture

Array of JSON

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Text input

Minimum watchersfilter/throttle

API API

combine/filter

network

convert eventsto strings

Data flowarchitecture

Filtered Array of JSON

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Text input

Minimum watchersfilter/throttle

API API

combine/filter

render

network

convert eventsto strings

Data flowarchitecture

Implementation in Bacon.js» http://jsfiddle.net/tehmou/2gxao3j4/5/

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Other input sources of an app» User navigates within the app

» Friends list is refreshed in the background

» Message delivery fails

» Application is suspended

» FarmVille request arrives

Values/events can go into the system only from the designated entry points.

that’s a period

More complexapplications

NetworkObservable

Disk store

parse cache

get additional information

Network again

View logic

View

Why You Should do It?» Cleaner code

» Makes you understand how your application really works

» .. or how it is supposed to work, at least

» Bugs are easier to track

Resources» My technical blog post for RxJava:

http://blog.futurice.com/top-7-tips-for-rxjava-on-android

» RxMarbles for understanding stream operations: http://rxmarbles.com/

» Original Rx: http://msdn.microsoft.com/en-gb/data/gg577609.aspx

» For JavaScript: http://baconjs.github.io/ or https://github.com/Reactive-Extensions/RxJS

Timo TuominenSoftware Consultant@tehmoutimo.tuominen@gmail.com+44 7404 948860

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