Block parameters in Ruby - Step-by-Step Execution

Concept Flow - Block parameters

Start method call with block

↓

Yield to block with parameters

↓

Block receives parameters

↓

Block executes with parameters

↓

Return to method after block

↓

Method continues or ends

The method calls a block and passes values to it as parameters. The block receives these parameters and runs its code using them.

Execution Sample

Ruby

def greet
  yield("Alice", 30)
end

greet do |name, age|
  puts "Name: #{name}, Age: #{age}"
end

This code calls a method that yields two values to a block, which receives them as parameters and prints them.

Execution Table

Step	Action	Block Parameters	Block Execution	Output
1	Call greet method	-	-	-
2	Inside greet, yield with ("Alice", 30)	name = "Alice", age = 30	puts "Name: Alice, Age: 30"	Name: Alice, Age: 30
3	Return from block to greet	-	-	-
4	greet method ends	-	-	-

💡 Method ends after block execution completes

Variable Tracker

Variable	Start	After yield
name	-	"Alice"
age	-	30

Key Moments - 2 Insights

Why do we write |name, age| inside the block?

The block parameters |name, age| receive the values passed by yield. See execution_table step 2 where yield sends "Alice" and 30, which the block captures as name and age.

What happens if the block parameters don't match the number of yielded values?

Ruby assigns values in order; extra yielded values are ignored, missing ones become nil. This is shown in execution_table step 2 where parameters match exactly.

Visual Quiz - 3 Questions

Look at the execution_table step 2, what value does the block parameter 'age' have?

A 30

B "Alice"

C nil

D 0

💡 Hint

Check the 'Block Parameters' column in step 2 of execution_table

At which step does the block print the output?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Block Execution' and 'Output' columns in execution_table

If we change yield("Bob", 25) in the method, what will the block parameter 'name' be at step 2?

A "Alice"

B "Bob"

C 25

D nil

💡 Hint

The block parameters get values from yield as shown in variable_tracker and execution_table step 2

Concept Snapshot

Block parameters receive values passed by yield inside a method.
Syntax: method calls yield with values, block declares parameters with |param1, param2|.
Block runs using these parameters.
If parameters mismatch, Ruby assigns in order or nil.
Blocks allow flexible code reuse with passed-in data.

Full Transcript

This example shows how Ruby methods can pass values to blocks using block parameters. The method greet calls yield with two values: "Alice" and 30. The block receives these values as parameters named name and age. Inside the block, it prints the name and age. The execution table traces each step: calling the method, yielding values, block execution with parameters, and method end. Variable tracker shows how name and age get assigned after yield. Key moments clarify why block parameters are needed and what happens if they don't match yielded values. The quiz tests understanding of parameter values and execution steps. This helps beginners see how blocks receive and use parameters step-by-step.