In Ruby, redo and retry are two powerful flow control mechanisms that allow developers to manipulate the execution of loops and exception handling blocks. These statements provide unique ways to repeat iterations or retry code execution in specific scenarios.

The redo Statement

The redo statement is used within loops to restart the current iteration without checking the loop's condition. It's particularly useful when you need to re-execute the current iteration due to certain conditions.

Syntax and Usage

Here's a simple example demonstrating the use of redo in a Ruby While Loop:


count = 0
while count < 5
  puts count
  count += 1
  redo if count == 3
end

In this example, when count reaches 3, the redo statement causes the loop to restart the current iteration, printing 2 twice.

Common Use Cases

Retrying user input when invalid data is provided
Reprocessing data that didn't meet certain criteria
Implementing custom iteration logic in complex scenarios

The retry Statement

The retry statement is primarily used in exception handling blocks to re-execute the entire begin section of a begin-rescue-end block.

Syntax and Usage

Here's an example of using retry in exception handling:


attempts = 0
begin
  puts "Attempting to do something..."
  raise "An error occurred" if attempts < 3
  puts "Success!"
rescue
  attempts += 1
  puts "Attempt #{attempts} failed. Retrying..."
  retry if attempts < 3
end

In this example, the code in the begin block is retried up to three times if an exception occurs.

Best Practices

Use retry judiciously to avoid infinite loops
Implement a maximum retry count to prevent excessive retries
Consider using retry for transient errors, such as network issues

Considerations and Caveats

While redo and retry are powerful tools, they should be used carefully:

redo can lead to infinite loops if not properly controlled
retry should be used sparingly in exception handling to avoid masking underlying issues
Overuse of these statements can make code harder to read and maintain

Understanding when and how to use redo and retry can greatly enhance your Ruby programming skills. These statements provide fine-grained control over program flow, allowing for more robust and flexible code in certain situations.

Related Concepts

To further enhance your understanding of Ruby flow control, consider exploring these related topics:

Ruby break and next for additional loop control mechanisms
Ruby raise Exceptions to learn more about exception handling
Ruby ensure Clause for guaranteed execution in exception handling blocks