I'm finding myself passing a lot of variables to my methods as named arguments as it makes things a lot clearer:
doFunction(name: 'Jack', age: 27)
now in doFunction I often find myself doing this:
doFunction(Map args) {
if (args['name']) {
def name = args['name']
// do stuff with name
}
}
Is there a language feature to unwrap the Map to its respective parameters on the fly? I couldn't find anything like that. and if there wasn't, I'm curious as to why, it seems like this is the natural Groovy approach to boilerplate.
I'd like a way to immediately check and work on the parameter if it exists, is there a cleaner way to do this? am I approaching Map arguments the wrong way entirely?
Since there is no destructuring like e.g. in clojure, one way to work with maps like this would be using with. Like:
void destruct(Map params) {
params.with{
if (name) {
println "Hello $name"
}
if (age) {
println "I am $age years old"
}
}
}
destruct name: "World", age: 4.54e9
// => Hello World
// => I am 4.54E+9 years old
destruct name: "Computer"
// => Hello Computer
Also on the nitpicking side: those are no named arguments (like e.g. in python). It is just a syntactic sugar for passing maps. E.g. it is short for destruct([name: 'World']) -- it will not work for a method void destruct(String name, BigDecimal age)
Related
So traits are a very cool feature, but I want to see how I could use them as plugins to a DSL I'm working on. But using traits in this manner would mean adding traits at runtime. The docs clearly demonstrate how to do that using:
def combinedTraits = person.withTraits TraitA, TraitB
Which is great, but it's all done with dynamic typing which makes it hard for IDEs to help with code-completion or to use CompileStatic. The only way I can figure how this might work in a type-safe way would be if Groovy had Type Unions. I'm trying to create a DSL akin to the following:
pipeline( Plugin1, Plugin2 ) {
step("Step1") { Map row ->
accept( row )
}
methodFromPlugin1("....", 123)
methodFromPlugin2("....", 456)
}
Then in the DSL doing the following:
public class PipelineDsl {
void pipeline( List<Class> traits, Closure closure ) {
closure.resolveStrategy =
closure.delegate = this.withTraits( traits )
closure.call()
}
}
But if I wanted to help the IDE out so code completion would work I'd need to add #DelegatesTo annotation on the Closure parameter, and I can't hard code the Traits there. An alternative version might be this:
pipeline {
step("Step1") { Map row ->
}
fromPlugin( Plugin1 ) { Plugin1 p ->
p.methodFromPlugin1("....", 123)
}
fromPlugin( Plugin2 ) { Plugin2 p ->
p.methodFromPlugin2("....", 456)
}
}
A little more clunky because I have to declare the parameter types on the Closures, and I can't easily use annotations provided to simplify it (#DelegatesTo, or #ClosureParam, etc).
Although this model mirrors Gradle's task name(type: PluginTask) {...} definitions for plugins and IDEs generally can follow along with those. But I can't tell what Gradle is doing to help out with that. And if I could simplify the clunky case (say remove the type on the Closure parameter) then I'd be able to implement the more elegant case too.
Any better ideas?
Newbie Alert! I feel silly asking this question but I need someone to teach me the correct syntax.
I have code that looks like this:
let thing: INewThing;
thing.personId = another.personId;
thing.address = another.work.address;
thing.greades = another.subjectInfo.grades;
thing.isCurrent = another.student.isCurrent;
I know it can be written cleaner. I want to use a lamda expression, something like this:
let thing: INewThing => {
personId = another.personId,
address = another.work.address,
grades = another.subjectInfo.grades,
isCurrent = another.student.isCurrent
} as IThingUpdate;
I have looked and looked for an example. I have yet to find one that works for me. It's just syntax but no matter what I try it doesn't work.
You're just looking to create a new object, which is a pretty different thing from a "lambda" (function). Just declare the object. You don't need a function.
const thing = {
personId: another.personId,
address: another.work.address,
// use the correct spelling below - no 'greades'
grades: another.subjectInfo.grades,
isCurrent: another.student.isCurrent,
};
If the another is typed properly, that should be sufficient.
If the another object had more properties using the same path, another option would be to destructure those properties out, then declare the object with shorthand, eg:
const originalObj = { prop: 'val', nested: { foo: 'foo', bar: 'bar', unwanted: 'unwanted' } };
const { foo, bar } = originalObj.nested;
const thing = { foo, bar };
Destructuring like this, without putting the values into differently-named properties, helps reduce typos - if a property starts out, for example, as someLongPropertyName, putting it into a standalone identifier someLongPropertyName and then constructing an object with shorthand syntax ensures that the new object also has the exact property name someLongPropertyName (and not, for example, someLongPRopertyName - which isn't that uncommon of a mistake when using the more traditional object declaration format).
But since all the paths in your another object are different, this approach wouldn't work well in this particular situation.
Actually I'm experimenting writing a DSL with groovy. So far ...
There are some things unclear to be regarding delegation and intercepting unwanted (Closure) structures:
first of all: How can I throw a (type of?) Exception to point to the correct line of code in the DSL that fails?
assuming
abstract MyScript extends Script {
def type(#DelegateTo(MyType) Closure cl) {
cl.delegate = new MyType()
cl()
this
}
}
under
new GroovyShell(this.class.classLoader, new CompilerConfiguration(scriptBaseClass: MyScript.name)).evaluate(…)
the passed DSL / closure
type {
foo: "bar"
}
passes silently.
I'm aware of, that foo: is just a POJ label but I'm not that sure what that defined Closure is interpreted as?
Neither did I found anything regarding the AST metaprogramming to get in touch of any defined labels to use them?
giving in
type {
foo = "bar"
}
it's clear that he will try to set the property foo, but do I really have to intercept unwanted fields/props by
class MyType {
def propertyMissing(String name) {
… // where I'm unable to println name since this leads to field access 'name' ...
}
}
while user is still allowed to pass
type {
foo "bar"
}
which leads to method not defined .. so I have to write additionally some metaClass.methodMissing or metaClass.invokeMethod stuff ..
meanwhile I tend to dismiss any closures in my dsl only working with simple
def type(Map vars) {
store << new MyType(vars)
// where in the constructor I was forced to write metaClass stuff to validate that only fields are given in the map that are defined in the class
}
that works, but both drafts are not what I expected to do when reading "groovy is so great for making DSLs" ...
I would experiment with the different options and then settle for one.
To guide your users you should give feedback similar to that of the regular compiler (i.e. line-number and column, maybe the expression).
Enforcing the correctness of the input can be non-trivial -- depending on your DSL.
For example:
type {
foo: "bar"
}
Is just a closure that returns the String bar. Is that something your user is supposed to do? The label will be part of the AST, AFAIK in org.codehaus.groovy.ast.stmt.Statement.statementLabels. If you want this syntax to assign something to foo then you'll need to rewrite the AST. The Expression could become a Declaration for the local Variable foo or could become an assignment for the Field foo. That's really up to you, however, Groovy gives you some capabilities that make creating a DSL easier:
You already used #DelegateTo(MyType) so you could just add a Field foo to MyType:
class MyType {
String foo
}
And then either use #CompileStatic or #TypeChecked to verify your script. Note that #CompileStatic will deactivate Run-time Metaprogramming (i.e. propertyMissing etc. won't be called anymore.) while #TypeChecked does not. This, however, will only verify Type-Correctness. That is: assigning to anything but a declared Field will fail and assigning an incompatible Type will fail. It does not verify that something has been assigned to foo at all. If this is required you can verify the contents of the delegate after calling the Closure.
I want to implement an 'active' flag for rules in my DSL. Here's how I wanted it to look like:
Shipping("Standard") {
active: true
description: "some text"
rules {
... define rules here
}
}
Here's how I got everything running following several tutorials:
Script dslScript = new GroovyShell().parse(new File("Standard"))
dslScript.metaClass.Shipping = { String name, Closure cl ->
ShippingDelegate delegate = new ShippingDelegate()
delegate.name = name
cl.delegate = delegate
cl.setResolveStrategy Closure.DELEGATE_FIRST
cl()
}
dslScript.run()
ShippingDelegate is simple:
class ShippingDelegate {
String name
void rules(Closure cl) {
... do stuff here
}
}
It all runs fine without complaints but how can I access 'active' or 'description'?
What does this syntax actually do anyway? It looks like a map assignment, but there is none. Or does the groovy compiler treat it as an incomplete ternary operator?
May I suggest a small change in your DSL so that your design can be simplified?
Edited, it is not clear in you example if you have more than one shipping instance. In my second try, I assume that the answer is yes
class ShippingRules {
boolean active
String description
String name
ShippingRules(String name) {
this.name=name
}
def rules(Closure c) {
c.delegate=this
c()
}
}
abstract class ShippingRulesScript extends Script {
def shipppingRules =[]
def shipping(String name, Closure c) {
def newRules=new ShippingRules(name)
shipppingRules << newRules
c.delegate=newRules
c()
}
}
def cfg= new CompilerConfiguration(
scriptBaseClass:ShippingRulesScript.name
)
Script dslScript = new GroovyShell(cfg).parse(new File("Standard"))
dslScript.run()
The DSL should be changed to this:
shipping("Standard") {
active= true
description= "some text"
rules {
... define rules here
}
}
shipping("International") {
active= true
description= "some text"
rules {
... define rules here
}
}
I.e. lose the capital to shipping, and use assignments instead of colons.
You would then later be able to retrieve the shipping rules from your dslScript shippingRules variable.
disclaimer: I cannot test my code right now, so there may be some typos in the code, but you get the general idea: use a base class where you provide your rules and properties to your script.
I asked a similar question on Google+, see here.
The summary is: you can use the map syntax only on constructors (ctors) and as function parameters.
Interesting is that it doesn't throw an exception.
As new to groovy...
I'm trying to replace the java idiom for event listeners, filters, etc.
My working code in groovy is the following:
def find() {
ODB odb = ODBFactory.open(files.nodupes); // data nucleus object database
Objects<Prospect> src = odb.getObjects(new QProspect());
src.each { println it };
odb.close();
}
class QProspect extends SimpleNativeQuery {
public boolean match(Prospect p) {
if (p.url) {
return p.url.endsWith(".biz");
}
return false;
}
}
Now, this is far from what I'm used to in java, where the implementation of the Query interface is done right inside the odb.getObjects() method. If I where to code "java" I'd probably do something like the following, yet it's not working:
Objects<Prospect> src = odb.getObjects( {
boolean match(p) {
if (p.url) {
return p.url.endsWith(".biz");
}
return false;
}
} as SimpleNativeQuery);
Or better, I'd like it to be like this:
Objects<Prospect> src = odb.getObjects(
{ it.url.endsWith(".biz") } as SimpleNativeQuery
);
However, what groovy does it to associate the "match" method with the outer script context and fail me.
I find groovy... groovy anyways so I'll stick to learning more about it. Thanks.
What I should've asked was how do we do the "anonymous" class in groovy. Here's the java idiom:
void defReadAFile() {
File[] files = new File(".").listFiles(new FileFilter() {
public boolean accept(File file) {
return file.getPath().endsWith(".biz");
}
});
}
Can groovy be as concise with no additional class declaration?
I think it would have helped you to get answers if you'd abstracted the problem so that it didn't rely on the Neodatis DB interface -- that threw me for a loop, as I've never used it. What I've written below about it is based on a very cursory analysis.
For that matter, I've never used Groovy either, though I like what I've seen of it. But seeing as no one else has answered yet, you're stuck with me :-)
I think the problem (or at least part of it) may be that you're expecting too much of the SimpleNativeQuery class from Neodatis. It doesn't look like it even tries to filter the objects before it adds them to the returned collection. I think instead you want to use org.neodatis.odb.impl.core.query.criteria.CriteriaQuery. (Note the "impl" in the package path. This has me a bit nervous, as I don't know for sure if this class is meant to be used by callers. But I don't see any other classes in Neodatis that allow for query criteria to be specified.)
But instead of using CriteriaQuery directly, I think you'd rather wrap it inside of a Groovy class so that you can use it with closures. So, I think a Groovy version of your code with closures might look something like this:
// Create a class that wraps CriteriaQuery and allows you
// to pass closures. This is wordy too, but at least it's
// reusable.
import org.neodatis.odb.impl.core.query.criteria;
class GroovyCriteriaQuery extends CriteriaQuery {
private final c;
QProspect(theClosure) {
// I prefer to check for null here, instead of in match()
if (theClosure == null) {
throw new InvalidArgumentException("theClosure can't be null!");
}
c = theClosure;
}
public boolean match(AbstractObjectInfo aoi){
//!! I'm assuming here that 'aoi' can be used as the actual
//!! object instance (or at least as proxy for it.)
//!! (You may have to extract the actual object from aoi before calling c.)
return c(aoi);
}
}
// Now use the query class in some random code.
Objects<Prospect> src = odb.getObjects(
new GroovyCriteriaQuery(
{ it.url.endsWith(".biz") }
)
)
I hope this helps!
I believe your real question is "Can I use closures instead of anonymous classes when calling Java APIs that do not use closures". And the answer is a definite "yes". This:
Objects<Prospect> src = odb.getObjects(
{ it.url.endsWith(".biz") } as SimpleNativeQuery
);
should work. You write "However, what groovy does it to associate the "match" method with the outer script context and fail me". How exactly does it fail? It seems to me like you're having a simple technical problem to get the solution that is both "the groovy way" and exactly what you desire to work.
Yep, thanks y'all, it works.
I also found out why SimpleNativeQuery does not work (per Dan Breslau).
I tried the following and it worked wonderfully. So the idiom does work as expected.
new File("c:\\temp").listFiles({ it.path.endsWith(".html") } as FileFilter);
This next one does not work because of the neodatis interface. The interface does not enforce a match() method! It only mentions it in the documentation yet it's not present in the class file:
public class SimpleNativeQuery extends AbstactQuery{
}
Objects<Prospect> src = odb.getObjects(
{ it.url.endsWith(".biz") } as SimpleNativeQuery
);
In the above, as the SimpleNativeQuery does not have a match() method, it makes it impossible for the groovy compiler to identify which method in the SimpleNativeQuery should the closure be attached to; it then defaults to the outer groovy script.
It's my third day with groovy and I'm loving it.
Both books are great:
- Groovy Recipes (Scott Davis)
- Programming Groovy (Venkat Subramaniam)