Yield to execute blocks in Ruby - Step-by-Step Execution

Concept Flow - Yield to execute blocks

Define method with yield

↓

Call method

↓

Inside method: execute code before yield

↓

Yield: pause method, run block passed

↓

Block runs: executes block code

↓

Return to method after yield

↓

Execute code after yield

↓

Method ends

The method runs code, then pauses at yield to run the passed block, then continues after the block finishes.

Execution Sample

Ruby

def greet
  puts "Hello"
  yield
  puts "Goodbye"
end

greet { puts "How are you?" }

This code defines a method that prints 'Hello', then runs a block, then prints 'Goodbye'.

Execution Table

Step	Action	Output	Notes
1	Call greet method		Method starts execution
2	puts "Hello"	Hello	Prints greeting
3	yield to block		Pauses method, runs block
4	Block runs: puts "How are you?"	How are you?	Block code executes
5	Return to method after yield		Method resumes
6	puts "Goodbye"	Goodbye	Prints farewell
7	Method ends		Execution complete

💡 Method finishes after printing 'Goodbye'

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
No variables	-	-	-	-

Key Moments - 2 Insights

Why does the block code run between the two puts statements?

Because the method uses yield at step 3 to pause and run the block, then continues after the block finishes (see execution_table rows 3-5).

What happens if no block is given when calling the method?

The method will raise an error at yield because it expects a block to run. You can check with block_given? to avoid this.

Visual Quiz - 3 Questions

Look at the execution table, what is printed at step 4?

A "How are you?"

B "Goodbye"

C "Hello"

D Nothing

💡 Hint

Check the Output column at step 4 in the execution_table.

At which step does the method resume after running the block?

A Step 2

B Step 3

C Step 5

D Step 6

💡 Hint

Look at the Notes column for step 5 in the execution_table.

If we remove the yield line, what changes in the output?

A Only "Hello" is printed

B "Hello" and "Goodbye" are printed, block is not run

C Only the block output is printed

D Nothing is printed

💡 Hint

Yield is the only place where the block runs, so without it the block code is skipped.

Concept Snapshot

def method
  code before yield
  yield  # runs block passed to method
  code after yield
end

Calling method with a block runs the block at yield.
Without yield, block is not executed.

Full Transcript

This example shows how Ruby's yield keyword lets a method run a block of code passed to it. The method greet prints 'Hello', then yield pauses the method and runs the block which prints 'How are you?'. After the block finishes, the method resumes and prints 'Goodbye'. The execution table traces each step and output. Key points: yield runs the block inside the method, and the method continues after yield. If no block is given, yield causes an error unless checked. Removing yield means the block never runs. This helps write flexible methods that can run custom code blocks.