Ruby Loops: Syntax For All Possible Approaches
Ruby comes with many statements and methods designed for looping. This amount can astonish both fledgling coders and developers experienced in other programming languages. In this post you'll be introduced to all ways of creating a loop in Ruby.
The list of Ruby loops
loop
This is the simplest technique of creating a loop:
"I'm in loop" will be output infinitely. To prevent it, we can use the break statement
each
All classes that include enumerable module have to define an each method. In case of Array class, it calls the given block one time for every single element
for
The for loop in Ruby is just syntax sugar for the each method. Output of this code will be same as above
Keep in mind that the iterator variable still lives after the for loop is finished
Ruby does not allow to access the block's parameter outside it, so code like this:
Raises the exception, if i variable is not defined anywhere else
undefined local variable or method `i' for main:Object (NameError)
Most of Rubyists avoid the for loop because the visibility of the iterator variable outside the loop is confusing in more complicated programs
while
It'll execute code block while condition is true
until
This loop is similar to the while loop, except that, it works while condition is false
In while/until statements do keyword is optional, so feel free to skip it
You can think about while/until loops as a repeating if/unless statements
times
Handy method if you know exactly how many times to execute a block
step
Passes each nth element to the block
upto
Passes to block each number, starting from number on which we call this method, up to limit defined in argument
downto
Opposite of above method
break
Already introduced in this post. Helpful in preventing creation of infinite loops or finishing them before condition
next
Skips to the next iteration
redo
Restarts the current iteration
It doesn't check loop condition, so it's easy to create infinite loop
Summary
As you can see loops in Ruby works slightly different than in other programming languages. Above examples seems quite simple, however, what's going under the hood confuses many newcomers. To gain a real understanding you must know how to work with blocks and understand object-orientation of this language.
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