Agenda

0. Demo

What are we going to create?

We are creating utility to unfurl links from webpages with ability to extend with custom logic.

1. Init app

https://crystal-lang.org/docs/installation/ https://crystal-lang.org/docs/ https://crystal-lang.org/api/0.25.1/

Tools:

http://crystalshards.xyz/ https://github.com/veelenga/awesome-crystal https://github.com/crystal-community/icr

2. Code structure

• shards / shard.yml
• .gitignore
• simple hello
• shards

3. Configure guardian:

https://github.com/f/guardian

• rerun app on change (for web apps it's better to use sentry)
• install shards automatically
• run specs on change
• run static code analysis (https://github.com/veelenga/ameba)

4. Ruby diff

• require ./, **
• visibility modifiers (private/protected/public)
• new types (tuple / named tuple)
• arithmetic overflow
• "safe" by default (first vs. first?)
• &. is better
• &&, ||
• single method with proper english
• method overloading
• auto keyword arguments
• previous_def / alias
• stdlib
• ...

https://docs.google.com/presentation/d/1XeIRwl1Y9IUAxsFdmUmRjpLl1CrIzRgFo5wdWJrsYTc

5. Design the lib/app

classes:

• Link
• Resolver/Strategy (abstract)
• Config

Usage:

link = Unfurl::Link.new(uri)
link.unfurl

Configuration:

• allow to specify list of resolvers

Resolver:

• matches?
• resolve

Unfurling:

FOR EACH resolver:
    IF resolver matches uri THEN
        resolve uri
        IF result IS NIL THEN
            return NOT_FOUND, "message"
        ELSE
            return OK, "url"

WHEN no resolvers found:
    return ERROR, "message"

6. Refactor

• alias
• initializer list

Unfurling:

7. Extras https://github.com/luckyframework/habitat https://github.com/crystal-community/cossack https://github.com/waterlink/spec2.cr https://github.com/waterlink/mocks.cr