Is Groovy static or dynamic

Copyright © 2013 Russel Winder 1
Is Groovy Static or
Dynamic?
Russel Winder
email: russel@winder.org.uk
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twitter: @russel_winder
web: http://www.russel.org.uk

?

Prelude

Debate [d be t]ɪˈ ɪ
n
1. (Government, Politics & Diplomacy) a formal discussion, as in a legislative
body, in which opposing arguments are put forward
2. discussion or dispute
3. (Philosophy) the formal presentation and opposition of a specific motion,
followed by a vote
vb
1. to discuss (a motion), esp in a formal assembly
2. to deliberate upon (something) he debated with himself whether to go
[from Old French debatre to discuss, argue, from Latin battuere]
debater n
Collins English Dictionary – Complete and Unabridged © HarperCollins
Publishers 1991, 1994, 1998, 2000, 2003.

foment [f m nt]əˈ ɛ
vb (tr)
1. to encourage or instigate (trouble, discord, etc.); stir up
2. (Medicine) Med to apply heat and moisture to (a part of the body) to relieve
pain and inflammation
[from Late Latin f ment re, from Latin f mentum a poultice, ultimately fromō ā ō
fov re to foster]ē
fomentation [ f m n te n]ˌ əʊ ɛ ˈ ɪʃə n
fomenter n
Usage: Both foment and ferment can be used to talk about stirring up trouble:
he was accused of fomenting/fermenting unrest. Only ferment can be used
intransitively or as a noun: his anger continued to ferment (not foment); rural
areas were unaffected by the ferment in the cities
Publishers 1991, 1994, 1998, 2000, 2003

ferment
n [ f m nt]ˈ ɜː ɛ
1. (Life Sciences & Allied Applications / Biochemistry) any agent or substance,
such as a bacterium, mould, yeast, or enzyme, that causes fermentation
2. (Life Sciences & Allied Applications / Biochemistry) another word for
fermentation
3. commotion; unrest
vb [f m nt]əˈ ɛ
1. (Life Sciences & Allied Applications / Biochemistry) to undergo or cause to
undergo fermentation
2. to stir up or seethe with excitement
[from Latin fermentum yeast, from ferv re to seethe]ē
fermentable adj
fermentability n
fermenter n
Usage: See at foment
Publishers 1991, 1994, 1998, 2000, 2003

The intention of this session is to
foment debate.

Let the fomentation begin.

No not the fermentation.

Starting Point

2003
Groovy is created as the
dynamic symbiote to Java.

Dynamic languages have no typed variables.

static totallyDynamic(x, y) {
x * y
}

Duck typing:
The receiver of the message decides the
meaning of the message.

Operators are not messages to a
receiving object in Java…

…Java isn't really an object-oriented language.

Fortunately, Groovy decided to follow Smalltalk,
and have a meta-object protocol.

Groovy is truly object-oriented,
message passing is the operational semantic,
and all variables are references to objects.

x * y
transforms to
x.plus(y)
to realize message passing with method call.

Interesting Issue

Objects clearly have static types.

Java allows for despatch by signature,
i.e. methods can be overloaded.

Adding types to parameters is required
for despatch by signature.

static runtimeTyping(Number x, Number y) {
x * y
}

Groovy is an optionally typed language:
variables, not just function and method
parameters, may or may not be given a type.

Adding types works in harmony with
method overloading.

All type checking is at run time.
This is harmonious with duck typing.

Being up to date

2013
Groovy is the dynamic symbiote to Java,
and
Groovy can now be the static language
replacement for Java.

@TypeChecked
@CompileStatic

@TypeChecked
static staticTyping(x, y) {
x * y
}

Compile time interface conformance,
no duck typing.

✘✘

Groovy now has C++-style message passing.

@TypeChecked
static staticTyping(Number x, Number y) {
x * y
}

Enforce don't ask.

A totally different view of how computation
proceeds: a different computational model.

class ExpandoDynamic {
static void main(args) {
def x = new Expando()
x.multiply = { y -> x.data * y }
x.data = 'XX'
def y = 2
assert x * 2 == 'XXXX'
}
}

@TypeChecked
class ExpandoStatic {
static void main(args) {
def x = new Expando()
x.multiply = { y -> x.data * y }
x.data = 'XX'
def y = 2
assert x * 2 == 'XXXX'
}
}

Should a language support two disparate
computational models?

final class Thing {
final x
Thing(x) { this.x = x }
Thing multiply(Thing y) { new Thing(x * y.x) }
boolean equals(Thing y) { x == y.x }
boolean equals (Object y) { x == y }
String toString() { x.toString() }
}
x = new Thing('XX')
y = new Thing(2)
z = new Thing(2.0)
assert x * y == 'XXXX'
assert x * y == new Thing('XXXX')
assert x * z == 'XXXX'
assert x * z == new Thing('XXXX')
assert y * z == 4.0
assert y * z == new Thing(4.0)
assert z * y == 4.0
assert z * y == new Thing(4.0)

@TypeChecked
final class Thing {
final Integer x_i
final String x_s
Thing(Integer x) { this.x_i = x ; assert this.x_s == null }
Thing(String x) { this.x_s = x ; assert this.x_i == null }
Thing multiply(Thing y) {
if (x_i == null) { new Thing(StringGroovyMethods.multiply(x_s, (Number)y.x)) }
else { new Thing(x_i * y.x_i) }
}
Object getX() { x_i == null ? x_s : x_i }
boolean equals(Thing y) { x_i == null ? x_s == y.x_s : x_i == y.x_i }
boolean equals (Object y) { x == y }
String toString() { x.toString() }
}
x = new Thing('XX')
y = new Thing(2)
assert x * y == 'XXXX'
assert x * y == new Thing('XXXX')

Should a language do one thing well?

class Duck {
static main(args) {
def total = 1
def data = [2, 3]
try {
total += data.sum()
}
catch (MissingMethodException mme) {
total = 0
}
assert total == 6
}
}

@TypeChecked
class NotDuck {
static void main(String[] args) {
Integer total = 1
List data = [2, 3]
total += (Integer)data.sum()
assert total == 6
}
}

Should a language be all things…

…or should we embrace polyglot programming?

Groovy +
{
Java
Scala
Ceylon
Kotlin

Tooling and IDE support is a big issue.

Endnote

This is philosophizing.

Personal experience useful.
We are allowed to debate and (dis)agree.
Create a personal view.

What is really needed is some objective research.

Psychology of programming.
PPIG.

foment [f m nt]əˈ ɛ
vb (tr)
1. to encourage or instigate (trouble, discord, etc.); stir up
2. (Medicine) Med to apply heat and moisture to (a part of the body) to relieve
pain and inflammation
[from Late Latin f ment re, from Latin f mentum a poultice, ultimately fromō ā ō
fov re to foster]ē
fomentation [ f m n te n] nˌ əʊ ɛ ˈ ɪʃə
fomenter n
Usage: Both foment and ferment can be used to talk about stirring up trouble:
he was accused of fomenting/fermenting unrest. Only ferment can be used
intransitively or as a noun: his anger continued to ferment (not foment); rural
areas were unaffected by the ferment in the cities
Publishers 1991, 1994, 1998, 2000, 2003

ferment
n [ f m nt]ˈ ɜː ɛ
1. (Life Sciences & Allied Applications / Biochemistry) any agent or substance,
such as a bacterium, mould, yeast, or enzyme, that causes fermentation
2. (Life Sciences & Allied Applications / Biochemistry) another word for
fermentation
3. commotion; unrest
vb [f m nt]əˈ ɛ
1. (Life Sciences & Allied Applications / Biochemistry) to undergo or cause to
undergo fermentation
2. to stir up or seethe with excitement
[from Latin fermentum yeast, from ferv re to seethe]ē
fermentable adj
fermentability n
fermenter n
Usage: See at foment
Publishers 1991, 1994, 1998, 2000, 2003

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