Closures

Closures are like lambdas in java, but slightly different.

For beginners

You may know what a method is. A method is a set order of instructions you can call. For example:

groovy

def print_numbers(int n) {
    for (def i : 0..n) {
        log.info(i)
    }
}

This method prints numbers from 0 to a given number to the log.

groovy

print_numbers(5)

This will now output

You can call that method as often as you want with any number input.

Now closures are methods, but you can carry them around. Example:

groovy

def print_numbers = { int n -> /*(1)!*/
    for (def i : 0..n) {
        log.info(i)
    }
}

Most of the time the type is optional, so here it would become { n -> ...

This closure does the same thing as the method above, but it's a variable instead of a method. Just like any other variable you can pass it to other methods. (See Events). You can invoke this closure the same way you do with a method:

groovy

print_numbers(3)

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