groovy as a dynamic language

Groovy as a Dynamic Language

Darren Cruse

(with just a smidge of metaprogramming)

Wednesday, April 22, 15

Agenda• Has Groovy arrived?

(what do you guys think?)

• Groovy as a “Dynamic Language”

(groovy as part of the family of languages that includes smalltalk, perl, javascript, ruby, etc)

• Some metaprogramming code examples:

Adding “Ruby style” new methods to groovy

(if time brief look at): Auto-generating UML sequence diagrams from running a groovy script.


Survey 1

Which is more important to your company/projects:

a. Groovy as a language

b. Grails as a web framework

c. Both are equally important


Survey 2At my company we are using groovy:

a. Heavily as the primary language for a project.

b. Moderately as a complement to java.

c. Lightly for unit tests, throw away scripts, etc.

d. We are Evaluating groovy for possible future use.

e. We are Not Using Groovy.


indeed.com


image from: http://whiteafrican.com/tag/crossing-the-chasmWednesday, April 22, 15

http://whiteafrican.com/tag/crossing-the-chasm/

http://whiteafrican.com/tag/crossing-the-chasm/

Ease of Adoption(versus)

Benefits of Adoption

“Ease ofAdoption”

“Benefits of Adoption”

“Sweet spot ofinnovation”

Adapted From: The Myths of Innovation, by Scott Berkun


Dynamic Languages(are on my mind)

(Glenn Campbell song, 1973)


What is a“Dynamic Language”?

(Graeme Rocher and Bob Lee, from 2006)http://graemerocher.blogspot.com/2006/03/groovy-beanshell-dynamic-vs-scripting.html


http://graemerocher.blogspot.com/2006/03/groovy-beanshell-dynamic-vs-scripting.html

http://graemerocher.blogspot.com/2006/03/groovy-beanshell-dynamic-vs-scripting.html

“Dynamic Programming Language”(according to Wikipedia)

“Dynamic Programming Language describes a class of high level programming languages that execute at runtime many common behaviors that other languages might perform at compilation.”



Most Dynamic Languages:

• Are Dynamically Typed

• Have functions as “first class citizens”

• Allow modifications to types at runtime

• Support eval



And “Dynamically Typed” means:

“A programming language is dynamically typed when the majority of type checking is performed at run-time as opposed to compile time. In dynamic typing, values have types but variables do not.”


Some “Dynamic Languages”(according to Wikipedia)

ActionScript

BeanShell*

LispGroovy

JavaScript

Clojure VBScript

Matlab

Lua

Objective-C

Perl PHP

Python

Ruby

Smalltalk

Tcl

*I guess this means the bunny was right and wrong, at the very same time?Wednesday, April 22, 15

Going Back in the Way-Back Machine...


Or: What I learned from Perl(that I’ll admit to, and that served me well in

learning groovy, and javascript)

Back when I did C, I vaguely understood that among other things a compiler lays out things so that generated machine

code knows the offset of fields within a structure.

This is what makes the generated code fast.

But it also makes it inflexible, because offsets are set in stone at compile time.


Statically Compiled Languages(compile stuff into offsets that set like concrete)

struct student { int id; char *name; float percent;};

offset field+0 id+4 name+8 percent

C Code: Offsets used in generated code:

compiler


But Perl had a very different approach to classes and objects...

They were just a Map.

This seemed crude, but combined with first class functions, and the speed of edit/test versus edit/compile/test - I grew

to like Perl over C for many tasks.


$student = { id => 1, name => “Jason”, percent => 100.0};

key valueid 1

name Jasonpercent 100.0

Perl Code: Runtime data structure:

interpreter

Dynamic Languages(classes in data structures you can manipulate at run time)


I grew to feel...

Perl was to clay, as C,

was to concrete.


Modern languages still carry these distinctions

(though a little blurrier)

Java is still a high performance compiled statically typed language, but with more run-time-stuff than C had (e.g. the

Reflection api).

And I still relate to the metaprogramming possibilities of Groovy (Javascript, Ruby, Python, etc) by thinking “oh

yeah, it’s basically just a Map”.


Groovy is Special(because it’s a hybrid)

Groovy combines a static language (java) and a Dynamic (smalltalk/ruby/perl like) language into one.

Groovy’s classes wrap a Map-like soft and chewy Dynamic Language coating - i.e. “Metaclass” -around a hard candy Static Language core - i.e. a normal java Class.

(it’s like an M&M but inside out)


Java Class Core(fast but not so flexible)

Groovy Metaclass Coating(think map)


FINALLY(some code!)

(Glenn Campbell song, 1973)


Exercise: Add “Factory New” (or “Ruby Style New”)

Methods to Groovy

i.e. not:

def service = new ServiceClass();

but rather:

def service = ServiceInterface.new();


Why?

•Some argue that the “new” keyword as practiced by C, C++, and Java is flawed, e.g. see:

Java's new Considered HarmfulBy Jonathan Amsterdam, April 01, 2002http://drdobbs.com/184405016

•It’s an example of something that you can do pretty easily in groovy that would be extremely difficult in java.

•Esp. when you consider the result feels pretty much like a native language feature to the programmer using it.


http://drdobbs.com/184405016

http://drdobbs.com/184405016

From “Java’s new Considered Harmful”

In a nutshell, the problem with new is that it fails to encapsulate object creation.

def service = new ServiceClass();

no encapsulation!


So: let’s see if we can add “factory new” methods to groovy classes.

Along with a smidge of what Spring provides (e.g. configurable singletons and prototypes)

Without using a container - just groovy, from groovy scripts.


Code samples for this talk available at:

https://github.com/darrencruse/groovy-metaprogramming-samples




groovy as a dynamic language

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