groovy 3 and the new groovy meta object protocol in examples
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Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under aCreative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/1
Groovy 3 the new Meta Object Protocol
in examples
Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under aCreative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Jochen Theodorou, GoPivtoal Germany GmbH@JochenTheodorou
Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under aCreative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/2
… in certainly not enough examples
Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under aCreative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Jochen Theodorou, GoPivtoal Germany GmbH@JochenTheodorou
Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under aCreative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/3
What cannot go forwardgoes backwards.
Johann Wolfgang von Goethe (1749-1832), German PoetTranslation by Jochen Theodorou
“
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Goals:
■ Metaclass as Persistent Collection and Realms
● Better multi threading performance
● Allowing different versions of metaclasses for same class
■ Only internal metaclasses
● no „extends MetaClassImpl“ any more, instead like ExpandoMetaClass for everything
● Delegation instead of Inheritance
■ MOP Methods
● Names and Signatures change to avoid conflicts with normal methods
● GroovyObject becomes a marker interface or is removed
● All methods then optional and in different variants
● No exception controlled MOP any more
■ Others
● All operators available for meta programmings
● Based on invokedynamic and ClassValue (Java 7 becomes minimum)
Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under aCreative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/5
MOP Methods= in class defined methods to control MOP
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Overview:
■ Uncached:
● Difficulty: I did hear of Groovy
● methodMissing, methodIntercept, propertyMissing, propertyIntercept
■ Cached 1:
● Difficulty: Me, want more. Now!
● cacheMethodMissing, cacheMethodIntercept, cachePropertyMissing,
cachePropertyIntercept
■ Cached 2:
● Difficulty: I know what I do! Give me the full program!
● cacheMethodTarget, cachePropertyTarget
Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under aCreative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/7
MOP Methods – A Groovy BuilderGroovy 1 and Groovy 2
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Groovy Builder in Groovy 1/2
class XmlBuilder { def out
def methodMissing(String name, args) { out << "<$name>" if(args[0] instanceof Closure) {
args[0].delegate = this args[0].call() } else {
out << args[0].toString() } out << "</$name>"
}}
def xml = new XmlBuilder(out:System.out) xml.html {
head { title "Hello World" }
body { p "Welcome!" }
}
console output:
<html><head><title>Hello World</title></head><body><p>Welcome!
</p></body></html>
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Groovy Builder in Groovy 1/2
class XmlBuilder { def out
def methodMissing(String name, args) { out << "<$name>" if(args[0] instanceof Closure) {
args[0].delegate = this args[0].call() } else {
out << args[0].toString() } out << "</$name>"
}}
def xml = new XmlBuilder(out:System.out) xml.html {
head { title "Hello World" }
body { p "Welcome!" }
}
console output:
<html><head><title>Hello World</title></head><body><p>Welcome!
</p></body></html>
called if no method can be found for call
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Groovy Builder in Groovy 1/2
class XmlBuilder { def out
def methodMissing(String name, args) { out << "<$name>" if(args[0] instanceof Closure) {
args[0].delegate = this args[0].call() } else {
out << args[0].toString() } out << "</$name>"
}}
def xml = new XmlBuilder(out:System.out) xml.html {
head { title "Hello World" }
body { p "Welcome!" }
}
console output:
<html><head><title>Hello World</title></head><body><p>Welcome!
</p></body></html>
name = name of callargs = arguments of call
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Groovy Builder in Groovy 1/2
class XmlBuilder { def out
def methodMissing(String name, args) { out << "<$name>" if(args[0] instanceof Closure) {
args[0].delegate = this args[0].call() } else {
out << args[0].toString() } out << "</$name>"
} //implcit return !//implcit return !}
def xml = new XmlBuilder(out:System.out) xml.html {
head { title "Hello World" }
body { p "Welcome!" }
}
console output:
<html><head><title>Hello World</title></head><body><p>Welcome!
</p></body></html>The result of the call is theresult of methodMissing
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MOP Methods – A Groovy BuilderGroovy 3 Uncached
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Groovy Builder in Groovy 3 - Uncachedclass XmlBuilder {
def out MopResult methodMissing(String name, args) { out << "<$name>" If (args[0] instanceof Closure) {
args[0].delegate = this args[0].call() } else {
out << args[0].toString() } out << "</$name>"
return MopResult.VOID } }
def xml = new XmlBuilder(out:System.out) xml.html { head {
title "Hello World" } body {
p "Welcome!" } }
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Groovy Builder uncached - before and after
class XmlBuilder { def out
def methodMissing (String name, args) { out << "<$name>"
if(args[0] instanceof Closure) { args[0].delegate = this args[0].call()
} else { out << args[0].toString() }
out << "</$name>" }}
class XmlBuilder {
def out MopResult methodMissing (String name, args) {
out << "<$name>" If (args[0] instanceof Closure) { args[0].delegate = this
args[0].call() } else { out << args[0].toString() }
out << "</$name>" return MopResult.VOID }
}
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Groovy Builder uncached - before and after
class XmlBuilder { def out
def methodMissing (String name, args) { out << "<$name>"
if(args[0] instanceof Closure) { args[0].delegate = this args[0].call()
} else { out << args[0].toString() }
out << "</$name>" }}
class XmlBuilder {
def out MopResult methodMissing (String name, args) {
out << "<$name>" If (args[0] instanceof Closure) { args[0].delegate = this
args[0].call() } else { out << args[0].toString() }
out << "</$name>" return MopResult.VOID }
}
MopResult contains theresult of the call
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Groovy Builder uncached - before and after
class XmlBuilder { def out
def methodMissing (String name, args) { out << "<$name>"
if(args[0] instanceof Closure) { args[0].delegate = this args[0].call()
} else { out << args[0].toString() }
out << "</$name>" }}
class XmlBuilder {
def out MopResult methodMissing (String name, args) {
out << "<$name>" If (args[0] instanceof Closure) { args[0].delegate = this
args[0].call() } else { out << args[0].toString() }
out << "</$name>" return MopResult.VOID }
}
it can also transport errorsor that there is no result (VOID)
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MOP Methods – A Groovy BuilderGroovy 3 Cached
return how to get a result, instead of the result itself
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Ein Groovy Builder in Groovy 3 - Cached
class XmlBuilder {
def out def methodMissing
(String name, args) {
out << "<$name>"
if(args[0] instanceof Closure) {
args[0].delegate = this
args[0].call()
} else { out << args[0].toString()
} out << "</$name>"
}
}
class XmlBuilder {
def out
void cacheMethodMissing (GroovyCall call, String name)
{ call.chain {out << "<${name}>"}
if(call[0].isAssignableTo(Closure))
{ call[0].chain
{it.delegate = this} call[0].execute()
} else {
call[0].execute "toString" }
call.chain {out << "</${name}>"} }
}
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Ein Groovy Builder in Groovy 3 - Cached
class XmlBuilder {
def out def methodMissing
(String name, args) {
out << "<$name>"
if(args[0] instanceof Closure) {
args[0].delegate = this
args[0].call()
} else { out << args[0].toString()
} out << "</$name>"
}
}
class XmlBuilder {
def out
void cacheMethodMissing (GroovyCall call, String name)
{ call.chain {out << "<${name}>"}
if(call[0].isAssignableTo(Closure))
{ call[0].chain
{it.delegate = this} call[0].execute()
} else {
call[0].execute "toString" }
call.chain {out << "</${name}>"} }
}
since there is no resultwe return void
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Ein Groovy Builder in Groovy 3 - Cached
class XmlBuilder {
def out def methodMissing
(String name, args) {
out << "<$name>"
if(args[0] instanceof Closure) {
args[0].delegate = this
args[0].call()
} else { out << args[0].toString()
} out << "</$name>"
}
}
class XmlBuilder {
def out
void cacheMethodMissing (GroovyCall call, String name)
{ call.chain {out << "<${name}>"}
if(call[0].isAssignableTo(Closure))
{ call[0].chain
{it.delegate = this} call[0].execute()
} else {
call[0].execute "toString" }
call.chain {out << "</${name}>"} }
}
GroovyCall is created foreach uncached call
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Ein Groovy Builder in Groovy 3 - Cached
class XmlBuilder {
def out def methodMissing
(String name, args) {
out << "<$name>"
if(args[0] instanceof Closure) {
args[0].delegate = this
args[0].call()
} else { out << args[0].toString()
} out << "</$name>"
}
}
class XmlBuilder {
def out
void cacheMethodMissing (GroovyCall call, String name)
{ call.chain {out << "<${name}>"}
if(call[0].isAssignableTo(Closure))
{ call[0].chain
{it.delegate = this} call[0].execute()
} else {
call[0].execute "toString" }
call.chain {out << "</${name}>"} }
}
No argument objects here,only their rutime classes
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Some more details:
■ We provide a high-level API to let you express how to get to a result, not what the
result is – This allows caching in the first place
■ The to be cached method called can go through cacheMethodMissing more than
once. Reasons for that can be type changes for the arguments or the receiver
■ If you want to react different to different values of the same type, caching might be
not for you. (example: provide the method to be called as additional argument
instead)
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MOP Methods – A Groovy BuilderGroovy 3 MethodHandles
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Ein Groovy Builder in Groovy 3 – MethodHandles class XmlBuilder {
def out
private final MethodHandle outField = LOOKUP.findGetter....
void cacheMethodTarget
(GroovyCall call, String name)
{
call.chain(
GroovyInvoker.bind(outField,"leftShift","<${name}>"))
if (call.arg(0).isAsignableTo(Closure)) {
call.arg(0).chain(
GroovyInvoker.setProperty("delegate",this))
call.arg(0).execute()
} else {
call.arg(0).execute "toString"
}
call.chain(
GroovyInvoker.bind(outField,"leftShift","</${name}>"))
}
}
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Some Explanations:
■ Target is to produce a MethodHandle
■ GroovyCall high-level API is helping you here and can be mixed with MethodHandles
■ Of course the MethodHandles-API from Java7 is efficient and powerful, but also
difficult to understand and handle – for example because types have to match
exactly
■ Ultimately (and only for the most crazy people) we want to provide a way to give
your own bootstrap method and then design yourself what you do with the call. This
way you could for example completely emulate Javalogik and also speed (of course
there is still an overhead through invokedynamic)
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MOP Methods – Dynamic FinderGroovy 1 und Groovy 2
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Dynamic Finder in Groovy 1/2
class GORM {
// an array of dynamic methods that use regex
def dynamicMethods = [...]
def methodMissing (String name, args) {
def method = dynamicMethods.find { it.match(name) }
if (method) {
GORM.metaClass."$name" = { Object[] varArgs ->
method.invoke(delegate, name, varArgs)
}
return method.invoke(delegate, name, args)
}
else throw new
MissingMethodException(name, delegate, args)
}
}
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Dynamic Finder in Groovy 1/2
class GORM {
// an array of dynamic methods that use regex
def dynamicMethods = [...]
def methodMissing (String name, args) {
def method = dynamicMethods.find { it.match(name) }
if (method) {
GORM.metaClass."$name" = { Object[] varArgs ->
method.invoke(delegate, name, varArgs)
}
return method.invoke(delegate, name, args)
}
else throw new
MissingMethodException(name, delegate, args)
}
}
adds a meta method to metaClassfor each missing method
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Dynamic Finder in Groovy 1/2
class GORM {
// an array of dynamic methods that use regex
def dynamicMethods = [...]
def methodMissing (String name, args) {
def method = dynamicMethods.find { it.match(name) }
if (method) {
GORM.metaClass."$name" = { Object[] varArgs ->
method.invoke(delegate, name, varArgs)
}
return method.invoke(delegate, name, args)
}
else throw new
MissingMethodException(name, delegate, args)
}
}
makes the metaClassstay in memory
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The metaclass is in Groovy 1 and 2 actually linked to an instance, but has to be
saved in a global structure. That might use SoftReferences to avoid memory
problems, still garbage collection doesn't like such actions.
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MOP Methods – Dynamic FinderGroovy 3 Uncached
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Dynamic Finder in Groovy 3
class GORM {
// an array of dynamic methods that use regex
def dynamicMethods = [...]
MopResult methodMissing (String name, args) {
def method = dynamicMethods.find { it.match(name) }
if (method) {
GORM.metaClass."$name" = { Object[] varArgs ->
method.invoke(delegate, name, varArgs)
}
return MopResult.of (GroovyInvoker.invoke
(method, delegate, name, args))
}
else return MopResult.ERROR
}
}
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Dynamic Finder in Groovy 3
class GORM {
// an array of dynamic methods that use regex
def dynamicMethods = [...]
MopResult methodMissing (String name, args) {
def method = dynamicMethods.find { it.match(name) }
if (method) {
GORM.metaClass."$name" = { Object[] varArgs ->
method.invoke(delegate, name, varArgs)
}
return MopResult.of (GroovyInvoker.invoke
(method, delegate, name, args))
}
else return MopResult.ERROR
}
}
makes the metaClassstay in memory
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Dynamic Finder in Groovy 3
class GORM {
// an array of dynamic methods that use regex
def dynamicMethods = [...]
MopResult methodMissing (String name, args) {
def method = dynamicMethods.find { it.match(name) }
if (method) {
GORM.metaClass."$name" = { Object[] varArgs ->
method.invoke(delegate, name, varArgs)
}
return MopResult.of (GroovyInvoker.invoke
(method, delegate, name, args))
}
else return MopResult.ERROR
}
}
but not longer than the class GORM
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MOP Methods – Dynamic FinderGroovy 3 Cached
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Dynamic Finder in Groovy 3
class GORM {
// an array of dynamic methods that use regex
def dynamicMethods = [...]
void cacheMethodMissing (GroovyCall call, String name)
{
def method = dynamicMethods.find { it.match(name) }
if (method) {
call.chain (method, delegate, name)
}
else call.error()
}
}
metaClass stays unchanged
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Metaclass Versions and Views
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Recover old version of a metaclass
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
def oldMetaClass = A.metaClass.freeze()
A.metaClass.foo = {->2}
assert new A().foo() == 2
oldMetaClass.restore()
assert new A().foo() == 1
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Recover old version of a metaclass
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
def oldMetaClass = A.metaClass.freeze()
A.metaClass.foo = {->2}
assert new A().foo() == 2
oldMetaClass.restore()
assert new A().foo() == 1
handler for the meta classInstead of the meta class itself
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Recover old version of a metaclass
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
def oldMetaClass = A.metaClass.freeze()
A.metaClass.foo = {->2}
assert new A().foo() == 2
oldMetaClass.restore()
assert new A().foo() == 1
make handler keepingcurrent meta class version
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Recover old version of a metaclass
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
def oldMetaClass = A.metaClass.freeze()
A.metaClass.foo = {->2}
assert new A().foo() == 2
oldMetaClass.restore()
assert new A().foo() == 1set meta method
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Recover old version of a metaclass
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
def oldMetaClass = A.metaClass.freeze()
A.metaClass.foo = {->2}
assert new A().foo() == 2
oldMetaClass.restore()
assert new A().foo() == 1
restore old metaclass version
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Some explanations:
■ Before Groovy 3 we always mutate the metaclass
● Recovering an old state is difficult
● Isolating changes almost impossible
■ In Groovy 3 the metaclass is a persistent collection which you can reference by a
handler
● Handler can be set to always give the actual meta class
● Or to “freeze” to keep the actual version and then maybe restore later
In the long term this might actually allow to serialize meta class states
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Usage of Realms
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
realm {
A.metaClass.foo = {->2}
assert new A().foo() == 2
}
assert new A().foo() == 1
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Usage of Realms
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
realm {
A.metaClass.foo = {->2}
assert new A().foo() == 2
}
assert new A().foo() == 1
create sub realm
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Usage of Realms
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
realm {
A.metaClass.foo = {->2}
assert new A().foo() == 2
}
assert new A().foo() == 1
set new meta method
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Usage of Realms
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
realm {
A.metaClass.foo = {->2}
assert new A().foo() == 2
}
assert new A().foo() == 1only visible in subrealm
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Usage of Realms
class A{}
A.metaClass.foo = {->1}
assert new A().foo() == 1
realm {
A.metaClass.foo = {->2}
assert new A().foo() == 2
} // end of realm
assert new A().foo() == 1
return to parent realm
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Some Explanations:
■ A Realm is a set of metaclases separated from the normal program (or parent realm)
at the point of call
■ Changes inside the Realm stay in the Realm and its subrealms
■ Exiting a Realm means to discard all changes done in the Realm
Thought Usage:
● Libraries can isolate code and protect it from outside changes
● Lexicographic Categories
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And as always, there is by far not enough time
:(
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