find
method
Code Along: Building the ##Objectives
- Continue to practice using yield and blocks
- Gain a deeper understanding of
#find
##Code Along Exercise
Fork and clone this lab. You'll be coding your solution in lib/my_find.rb
. If at any point you want to follow along with the example, you can put a binding.pry
anywhere in the method and run ruby bin/my_find
in your terminal to pry around.
###Step 1
We need to iterate through each element in the passed in collection using the simple lower level iterator while
. Remember, since this is a lower level iterator, we will need to explicitly add a counter we'll call i
, and increment it each time we go into the loop (i = i + 1
):
def my_find(collection)
i = 0
while i < collection.length
i = i + 1
end
end
###Step 2
For each element in the collection, you're going to yield
to the block. Let's look at the code and break down what's happening.
def my_find(collection)
i = 0
while i < collection.length
yield(collection[i])
i = i + 1
end
end
When this code is run and it hits the yield
line, it is going to send whatever is passed in as the argument to the block.
Note: If you are confused about where the block comes from, it becomes clearer after the method is called. Here's an example:
collection = (1..100).to_a
my_find(collection) {|i| i % 3 == 0 and i % 5 == 0 }
As this code executes it will look like this:
def my_find(collection)
i = 0
while i < 100
yield(1)
i = i + 1
end
end
When it hits the yield(1)
, it is going to send 1
to the block, evaluate it, and send the return value back to yield
:
my_find(collection) {|1| 1 % 3 == 0 and 1 % 5 == 0 }
#=> false
In this example, ruby will send false
(the return value of the block) back to the my_find
method because 1 % 3 == 0 and 1 % 5 == 0
evaluates to false
.
###Step 3: Using the return value of the yield block
The purpose of the find
method is to return the first element in the array that evaluates to true
not the return value itself. Therefore, let's use the return value to set a conditional. In other words, we want to say something like:
- Yield to this block with the given argument
- If the block returns true,
return
the argument we passed into yield AKA the element in the array that evaluated to true. This will exit the loop and the element will be the return value of the method. - If the block returns false, continue to the next element in the array
def my_find(collection)
i = 0
while i < collection.length
if yield(collection[i])
return collection[i]
end
i = i + 1
end
end
We can refactor this slightly by putting our if
statement all on one line using a statement modifier:
def my_find(collection)
i = 0
while i < collection.length
return collection[i] if yield(collection[i])
i = i + 1
end
end
Sticking with our previous example:
collection = (1..100).to_a
my_find(collection) {|i| i % 3 == 0 and i % 5 == 0 }
Our method will return the first element in the array that evaluates to true
. In our example this would be 15.