Crystal

Like Ruby, but with types and stuff

👋🏼

About contempt

Outline

History / Basic intro
Technical background
Syntax / Features
Possibilities
The bad
Q&A

History / Basic intro

First commit Sep 2012

Goals

Have a syntax similar to Ruby (but compatibility with it is not a goal)
Statically type-checked but without having to specify the type of variables or method arguments.
Be able to call C code by writing bindings to it in Crystal.
Have compile-time evaluation and generation of code, to avoid boilerplate code.
Compile to efficient native code.

History / Basic intro

Reasons

We love Ruby's efficiency for writing code.

We love C's efficiency for running code.

We want the best of both worlds.

We want the compiler to understand what we mean without having to specify types everywhere.

We want full OOP.

Oh, and we don't want to write C code to make the code run faster.

History / Basic intro

How does it look?

Valid Ruby and Crystal!

History / Basic intro

What about performance?

21X

History / Basic intro

Technical background

Compilers are hard

Technical background

The LLVM Compiler Infrastructure

https://en.wikipedia.org/wiki/LLVM#/media/File:LLVM_Logo.svg

Technical background

Does (most of) the hard work!

Technical background

Hello World in LLVM IR

Technical background

It's easy to generate IR

https://www.slideshare.net/crystallanguage/crystal-internals-part-1-70673255

Technical background

Targets multiple archs (x86,x64,arm,ppc,wasm,etc.)
Project optimizations improve your compiler for free
Linker for ELF,PE,mach-O,etc
Standardized debugging

Syntax / Features

Everything is an object

Syntax / Features

Basic Types

Literal	Value
Nil	nil
Bool	true / false
Int32, Int64, Integer	1, -2, 19_i64, 8_u8
Float64, Float	1.0, 1.0_f32
Char	'a'
String	"a"
Symbol	:a
Array	[1,2], [] of Int32
Hash	{"a":1},{} of Symbol => Int32
Tuple	{1,"a",:b}

Syntax / Features

Arrays

Type inference! Union types!

Syntax / Features

Arrays

Quality error messages

Syntax / Features

Procs

Syntax / Features

Requiring code

GEM_HOME

If a file named "filename.cr" is found in the require path, it is required.
If a directory named "filename" is found and it contains a file named "filename.cr" directly underneath it, it is required.
If a directory named "filename" is found with a directory "src" in it and it contains a file named "filename.cr" directly underneath it, it is required.
If a directory named "filename" is found with a directory "src" in it and it contains a directory named "filename" directly underneath it with a "filename.cr" file inside it, it is required.
Otherwise a compile-time error is issued.

Just 'src' and 'lib' matter in the project root

Syntax / Features

Classes

Syntax / Features

Classes

Syntax / Features

Classes

Syntax / Features

Classes

Syntax / Features

Type aliases

Syntax / Features

Generics

Syntax / Features

Method overloading

Syntax / Features

Type fencing

Syntax / Features

Return types

Syntax / Features

Visibility

Syntax / Features

No $global vars!

Syntax / Features

C bindings

Syntax / Features

Finalizers

Syntax / Features

Structs

Structs inherit from Value so they are allocated on the stack and passed by value: when passed to methods, returned from methods or assigned to variables, a copy of the value is actually passed (while classes inherit from Reference, are allocated on the heap and passed by reference).

Therefore structs are mostly useful for immutable data types and/or stateless wrappers of other types, usually for performance reasons to avoid lots of small memory allocations when passing small copies might be more efficient

From the docs:

Syntax / Features

Enums