Define_method for dynamic methods in Ruby - Step-by-Step Execution

Concept Flow - Define_method for dynamic methods

Start

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Call define_method with name and block

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Ruby creates method dynamically

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Method can be called like normal

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Method executes block code

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End

This flow shows how Ruby's define_method creates a method dynamically and then allows calling it like a normal method.

Execution Sample

Ruby

class Greeter
  define_method(:hello) do |name|
    "Hello, #{name}!"
  end
end

puts Greeter.new.hello("Alice")

This code defines a method 'hello' dynamically that greets a person by name, then calls it.

Execution Table

Step	Action	Evaluation	Result
1	Call define_method(:hello) with block	Method 'hello' is created dynamically	Method 'hello' added to Greeter
2	Create Greeter instance	Instance created	#<Greeter:0x000...>
3	Call hello("Alice") on instance	Block runs with name='Alice'	"Hello, Alice!" returned
4	puts prints returned string	Output to console	Hello, Alice!

💡 Method call completed and output printed

Variable Tracker

Variable	Start	After define_method	After instance creation	After method call
hello (method)	undefined	defined as dynamic method	available on instance	executes block with argument
name (block param)	undefined	undefined	undefined	"Alice" during method call

Key Moments - 2 Insights

Why can we call 'hello' on the instance even though it was not defined with 'def'?

Because define_method dynamically creates the method and adds it to the class, making it callable like any normal method (see execution_table step 1 and 3).

What is the role of the block passed to define_method?

The block contains the code that runs when the dynamic method is called. It can take parameters and return values (see execution_table step 3).

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of calling hello("Alice")?

A nil returned

B Method not found error

C "Hello, Alice!" returned

D "hello" string returned

💡 Hint

Check execution_table row 3 for the method call result

At which step is the method 'hello' added to the Greeter class?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

See execution_table row 1 where define_method is called

If we change the block to return "Hi, #{name}", what changes in the execution_table output?

A Output changes to "Hi, Alice"

B Method creation fails

C No change in output

D Error at method call

💡 Hint

Output depends on the block code executed in step 3

Concept Snapshot

define_method(:name) { |params| ... } creates a method dynamically.
The method can be called like a normal method.
The block defines the method body.
Useful for dynamic or metaprogramming tasks.
Allows passing parameters and returning values.

Full Transcript

This example shows how Ruby's define_method creates a method dynamically inside a class. The method 'hello' is defined with a block that takes a name and returns a greeting string. When we create an instance of Greeter and call hello with 'Alice', the block runs and returns 'Hello, Alice!'. The method behaves like any normal method even though it was created dynamically. This is useful when you want to create methods on the fly based on conditions or data.