How to Use Closures In Groovy?

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In Groovy, closures are blocks of code that can be assigned to variables and passed around as arguments to functions. They are similar to anonymous functions or lambdas in other languages.


To create a closure in Groovy, you can use the -> syntax followed by the code block. For example:

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def add = { a, b -> 
    a + b 
}
println add(2, 3) // Output: 5


Closures can capture variables from their surrounding scope, making them a powerful tool for defining callback functions and handling asynchronous operations.


You can also define closures with multiple arguments and use them as method parameters.

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def greet = { name -> 
    println "Hello, $name!" 
}
greet("John") // Output: Hello, John!


In addition, closures can be used with higher-order functions like each, collect, find, etc. to perform operations on collections or manipulate data.

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def numbers = [1, 2, 3, 4, 5]
numbers.each { num -> println num * 2 }
// Output: 2 4 6 8 10


Overall, closures in Groovy provide a flexible and concise way to define and use functions within your code.

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How to create higher order functions with closures in Groovy?

In Groovy, you can create higher order functions with closures by defining a method that takes a closure as a parameter and then calling that closure within the method. Here's an example:

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// Define a higher order function that takes a closure as a parameter
def higherOrderFunction(Closure closure) {
    return closure
}

// Create a closure that doubles a number
def doubleClosure = { number -> number * 2 }

// Use the higher order function with the doubleClosure
def result = higherOrderFunction(doubleClosure)
println result(5) // Output will be 10


In this example, the higherOrderFunction takes a closure as a parameter and returns that closure. We then define a doubleClosure that doubles a number and pass it to the higherOrderFunction. Finally, we call the returned closure with a value of 5, which results in 10 being printed to the console.


This is a basic example of creating higher order functions with closures in Groovy. You can customize your higher order functions and closures based on your requirements.


What is the 'it' keyword used for in closures in Groovy?

In closures in Groovy, the 'it' keyword is used as a shorthand reference to the implicit parameter of the closure. This allows a more concise syntax when working with single-parameter closures. Instead of explicitly defining a parameter, you can refer to it simply as 'it'.


How to use closures with collections in Groovy?

In Groovy, closures can be used with collections in a variety of ways. Here are a few examples:

  1. Using the each() method: The each() method iterates over each element in a collection and applies the specified closure to each element. For example:
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def list = [1, 2, 3, 4, 5]
list.each { println it }


This code will print each element in the list.

  1. Using the collect() method: The collect() method creates a new collection by applying a closure to each element in the original collection. For example:
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def list = [1, 2, 3, 4, 5]
def squaredList = list.collect { it * it }


This code will create a new list where each element is the square of the corresponding element in the original list.

  1. Using the findAll() method: The findAll() method creates a new collection containing only the elements that satisfy a given condition specified by a closure. For example:
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def list = [1, 2, 3, 4, 5]
def evenList = list.findAll { it % 2 == 0 }


This code will create a new list containing only the even elements from the original list.


These are just a few examples of how closures can be used with collections in Groovy. Closures provide a powerful and flexible way to manipulate collections in a concise and readable manner.


How to use closures for partial application in Groovy?

In Groovy, you can use closures for partial application by creating a closure that accepts some of the arguments for a function and returns a new closure that holds those arguments until invoked with the remaining arguments.


Here's an example of how you can use closures for partial application in Groovy:

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def add = { a, b -> a + b }

// Partially apply the 'add' function with the first argument
def add3 = { add.curry(3) }

// Use the partially applied function
println add3(5) // Output: 8


In this example, we first define a closure named add that takes two arguments and returns their sum. Then, we create a new closure named add3 that partially applies the add function with the first argument set to 3. When we call add3 with the second argument (5), it returns the result of adding 3 and 5, which is 8.


This is how you can use closures for partial application in Groovy to create reusable functions with predefined arguments.


How to scope variables in closures in Groovy?

In Groovy, variables in closures can be scoped in a few different ways:

  1. Implicit scopes: Variables defined outside of a closure can be accessed from within the closure without any special syntax. This is known as the implicit scope.
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def x = 10
def myClosure = { println x }
myClosure() // Output: 10


  1. Explicit scopes: To explicitly scope a variable within a closure, you can use the def keyword to define the variable within the closure. This will create a new variable within the closure that is separate from any variables with the same name in an outer scope.
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def x = 10
def myClosure = { 
    def x = 20
    println x
}
myClosure() // Output: 20


  1. Using the owner property: You can access variables from the outer scope using the owner property of the closure. This allows you to explicitly reference variables from an outer scope within the closure.
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def x = 10
def myClosure = { println owner.x }
myClosure() // Output: 10


Overall, scoping variables in closures in Groovy is flexible and can be achieved using implicit or explicit scoping techniques depending on your specific requirements.

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