Closures Blocks and Procs in Ruby

What are closures in Ruby?

Closures in Ruby are self-contained code snippets that can be passed around and executed at a later time. They encapsulate both the code and the context in which they were created, allowing them to access variables and data from their surrounding scope even when executed elsewhere. Blocks, lambdas and procs serve as the building blocks of closures in Ruby, enabling developers to write flexible and reusable code. Some situations where closures can be used is while using iterators, event handling, and callbacks. They can be supplied as a block of code.

Understanding Blocks in Ruby

A block is a closure that can be associated with a method call. Consisting of a group of statements surrounded by either curly braces {} or the keywords do and end, blocks are primarily used for one-time execution within a method.

Definition and purpose of blocks

• Blocks in Ruby are sections of code that can be passed as arguments to methods, allowing for customizations and additional functionality without modifying the method itself.
• They promote a modular design approach by separating logic, improving code readability, maintainability, and modularity.
• They are commonly used in iteration methods like each, map, and select, enabling specific logic to be applied to each element of a collection, resulting in more expressive and readable Ruby code.
• Blocks can access variables and data from their surrounding scope, creating closures that retain their context. This feature facilitates code encapsulation and reusability while maintaining access to necessary context, even when executed in different contexts.

Creating a block in Ruby

A series of statements should be enclosed in curly braces or the do and end keywords to form a block. Depending on how the method is defined, blocks can either be explicitly or implicitly supplied to the method.

Block variables

• Block variables transfer data from the calling method to the block, residing only within the block's scope.
• They are defined within pipes (| |) at the start of the block declaration.
• Block variables can be used to pass data and customize the block's behavior based on the input.
• They enable dynamic development and customization of blocks.
• They are useful in iteration methods to access individual elements of a collection or specific parameters.

Example

Here’s an example of a basic block in Ruby that calculates the sum of three numbers provided to it:

Output

Explanation

In this example, the calculate_sum method uses the splat operator * to accept a variable number of inputs. It iteratively calculate the sum of the given values using the reduce method.

We can transform the sum calculation logic into a reusable function using this block-based technique. We can easily apply the sum calculation to any number of input values by utilizing the block to describe the calculation within the reduce method.

Understanding Procs in Ruby

Proc is an object that represents a block of code. It has the ability to store blocks of code in variables, pass them as arguments, and reuse them repeatedly. Procs allow programmers an easy way to create closures that can be changed and called independently. It becomes easier to create expressive and adaptable Ruby programs with procs.

Definition and purpose of procs

• Procs in Ruby are reusable chunks of code that package up blocks into first-class objects, allowing them to be assigned to variables.
• Procs offer flexibility and modularity, enabling developers to create portable and reusable code snippets.
• Procs can be passed as arguments to methods, allowing dynamic behavior and injection of custom functionality.
• They can contain return statements, enabling them to pass data or results back to the calling context, providing a form of control flow within the program.

Creating a proc in Ruby

To create a proc, we can use either the Proc.new or proc method, followed by the block of code we want to encapsulate. The resulting proc object can be assigned to a variable for later use. To consider an example for each case,

Assigning a proc to a variable

Procs can be created using the process we just discussed in the section above and directly assigned to variables, making them callable and reusable. Once assigned, the proc can be invoked using the call method, followed by any necessary arguments. This makes it reusable pretty easily, simply by passing different sets of arguments. As an example, for a proc generating a personalized greeting message, the call can be done as:

Output

Passing procs as arguments to methods

Procs in Ruby can be passed as arguments to methods, allowing behavior to be passed along with data and providing a way to handle varying scenarios without modifying the method's core implementation.

Example

Here is an illustration of how to create and use a proc in Ruby:

Output

Explanation

This example consists of a simple proc, called increment_and_double, which performs a mathematical operation defined by us. It takes a number as an argument, increment it by one, and double it. The result is then returned and displayed.

Lambdas as Closures

When it comes to encapsulating code into reusable units, lambdas are similar to procs. However, in terms of behavior and syntax, they do differ slightly from one another.

• The main difference lies in argument handling and return statements.
• Lambdas are strict with argument matching, requiring the exact number of parameters, while procs are more forgiving.
• Lambdas behave like methods in terms of return statements, while procs return from the enclosing method or block they are defined within.
• Lambdas use the -> operator for definition, distinguishing them from procs that use proc or Proc.new.

What are lambdas?

Lambdas are anonymous functions that can be assigned to variables or passed as arguments. The lambda keyword or the -> syntax is used to define lambdas in Ruby, and behave like methods. They can be considered as an advanced version of procs.

Syntax of lambda in Ruby

The lambda keyword or the -> syntax followed by the parameters and the code block is used to define a lambda. Let's see an example:

Difference between lambda and proc in Ruby

The main difference between lambdas and procs lies in how they handle return statements and argument checking. Lambdas perform argument checking, ensuring that correct number of arguments are passed. Additionally, lambdas return control to the calling method, whereas procs return immediately, bypassing the calling method.

Example

We can use the following as an illustration of the application of a lambda:

Output

Explanation

The method increment_and_double in this example accepts two numbers as parameters. The call method, which represented the desired operation, is used to invoke a lambda, and the outcome is returned and printed. Calling the lambda function with the wrong number of arguments will result in ArgumentError

Returning from Closures

Closures in Ruby can use the return keyword to send values back to the caller context. This allows for communication and data flow between the closure and its caller by allowing a closure to convey data or results back to the method or block that called it. The functionality of closures in Ruby are increased by the return statement since it permits control flow and makes information interchange easier.