Elegant way for do ... while in groovy
LoopsGroovyDo WhileLoops Problem Overview
How to do code something like this in groovy?
do {
x.doIt()
} while (!x.isFinished())
Because there is no do ... while syntax in groovy.
> No 'do ... while()' syntax as yet. > > Due to ambiguity, we've not yet added support for do .. while to Groovy
References:
Loops Solutions
Solution 1 - Loops
You can roll your own looping that's almost what you want.
Here's an example with loop { code } until { condition }
You can't have a corresponding loop { code } while { condition } because while is a keyword.
But you could call it something else.
Anyway here's some rough and ready code for loop until. One gotcha is you need to use braces for the until condition to make it a closure. There may well be other issues with it.
class Looper {
private Closure code
static Looper loop( Closure code ) {
new Looper(code:code)
}
void until( Closure test ) {
code()
while (!test()) {
code()
}
}
}
Usage:
import static Looper.*
int i = 0
loop {
println("Looping : " + i)
i += 1
} until { i == 5 }
Solution 2 - Loops
So many answers and not a single one without a redundant call, a shame ;)
This is the closest it can get to purely language syntax based do-while in Groovy:
while ({
x.doIt()
!x.isFinished()
}()) continue
The last statement within curly braces (within closure) is evaluated as a loop exit condition.
Instead of continue keyword a semicolon can be used.
Additional nice thing about it, loop can be parametrized (kind of), like:
Closure<Boolean> somethingToDo = { foo ->
foo.doIt()
!foo.isFinished()
}
and then elsewhere:
while (somethingToDo(x)) continue
Formerly I've proposed this answer over here: https://stackoverflow.com/questions/8188641/do-while-in-groovy-with-inputstream/22057667#22057667
Solution 3 - Loops
Depending on your use case, there are options like this: https://stackoverflow.com/questions/8188641/do-while-in-groovy
Or you can do:
x.doIt()
while( !x.finished ) { x.doIt() }
Or
while( true ) {
x.doIt()
if( x.finished ) break
}
Solution 4 - Loops
You can use a condition variable with the regular while loop:
def keepGoing = true
while( keepGoing ){
doSomething()
keepGoing = ... // evaluate the loop condition here
}
Solution 5 - Loops
Update Groovy 2.6 has been abandoned to concentrate on 3.0.
From Groovy 2.6 on, do-while is supported when enabling the new Parrot Parser, from Groovy 3.0 on this is the default. See [release notes][1]:
// classic Java-style do..while loop
def count = 5
def fact = 1
do {
fact *= count--
} while(count > 1)
assert fact == 120
[1]: http://groovy-lang.org/releasenotes/groovy-2.6.html "release notes"
Solution 6 - Loops
Or you can implement it in a Groovier way :
def loop(Closure g){
def valueHolder = [:]
g.delegate = valueHolder
g.resolveStrategy = Closure.DELEGATE_FIRST
g()
[until:{Closure w ->
w.delegate = valueHolder
w.resolveStrategy = Closure.DELEGATE_FIRST
while(!w()){
g()
}
}]
}
Solution 7 - Loops
By now, Groovy has support for do/while:
do {
x.doIt()
} while (!x.isFinished())