Block syntax (do..end and curly braces) in Ruby - Step-by-Step Execution

Concept Flow - Block syntax (do..end and curly braces)

Start

↓

Call method with block

↓

Ruby reads block syntax

↓

If do..end

↓

Execute block lines

↓

If curly braces

↓

Execute block lines

<--- Back to method↓

Method finishes

↓

End

↩<--- Back to method

Ruby methods can take blocks written with do..end or curly braces. Ruby reads the block, executes its lines, then returns to the method.

Execution Sample

Ruby

3.times do
  puts "Hi"
end

This code runs the block 3 times, printing "Hi" each time.

Execution Table

Step	Action	Block Syntax	Output
1	Call 3.times with block	do..end
2	Execute block iteration 1	do..end	Hi
3	Execute block iteration 2	do..end	Hi
4	Execute block iteration 3	do..end	Hi
5	Finish method	do..end

💡 All 3 iterations done, method ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final

Key Moments - 2 Insights

Why can we use both do..end and curly braces for blocks?

Both are block delimiters in Ruby. do..end is often used for multi-line blocks, curly braces for single-line, but both work the same as shown in the execution_table.

Does the block run immediately when passed?

No, the method (like times) controls when the block runs. The execution_table shows the method calls the block 3 times.

Visual Quiz - 3 Questions

Look at the execution_table, what is printed at Step 3?

A "Hi"

B "Hello"

C Nothing

D Error

💡 Hint

Check the Output column at Step 3 in the execution_table

At which step does the method finish running the block?

A Step 2

B Step 5

C Step 4

D Step 1

💡 Hint

Look at the Action column and Output column in the execution_table

If we replace do..end with curly braces, what changes in the output?

A Code breaks with error

B Output changes to "Hello"

C Output stays the same

D Block runs only once

💡 Hint

Refer to the concept_flow and key_moments about block syntax equivalence

Concept Snapshot

Ruby blocks can be written with do..end or curly braces.
Both delimit a block of code passed to methods.
Blocks run when the method calls them.
do..end is preferred for multi-line blocks.
Curly braces often used for single-line blocks.
Output depends on block code executed inside method.

Full Transcript

This lesson shows how Ruby uses blocks with two syntaxes: do..end and curly braces. When a method like times is called with a block, Ruby reads the block code inside the delimiters. The method controls how many times the block runs. For example, 3.times do puts "Hi" end runs the block 3 times, printing "Hi" each time. Both do..end and curly braces work the same way, with do..end often used for multi-line blocks and curly braces for single-line blocks. The execution table traces each step: calling the method, running the block 3 times, and finishing. This visual helps beginners see how blocks execute step-by-step.