Programming Ruby: The Pragmatic Programmers' Guide (Second Edition): Mechanics of the Method Call

In Ruby, a method call is not a static jump to a memory address; it is a dynamic Message-Passing event. When you invoke a method, you are sending a message to a Receiver. This message consists of the method name, optional arguments, and a potential Block Association.

1. Call Syntax & Ambiguity

Ruby allows great flexibility: Foo.Bar and Foo.Bar() are identical. However, Foo::Bar usually refers to a constant, while Foo::Bar() forces a method call. Parentheses are often omitted to create DSL-like experiences where methods look like properties.

2. Operator Deconstruction

Operators are actually Redefinable Methods. The expression expr1 + expr2 is sugar for (expr1).+(expr2). This applies to unary (-obj), binary (a < b), and suffix operators.

3. The yield Mechanism

Methods use yield to push control flow into the associated block. Using Kernel.block_given?, a method can dynamically decide how to handle logic based on the caller’s context.

TERMINAL bash — 80x24

> Ready. Click "Run" to execute.

QUESTION 1

In Ruby, what is syntactically equivalent to the expression a + b?

a.add(b)

a.+(b)

+(a, b)

Add.new(a, b)

QUESTION 2

What is the primary difference between Foo::Bar and Foo::Bar()?

None, they are identical.

The first is a class, the second is a module.

The first is typically a constant; the second is a method call.

The first is private, the second is public.

QUESTION 3

How does a method verify if it was called with a do...end or {...} block?

Using if block_exists?

By checking if the last argument is nil.

Using Kernel.block_given?

By catching a LocalJumpError.

✅ Correct!

block_given? is the standard predicate for checking block presence.

❌ Incorrect

Ruby provides block_given? specifically for this purpose within any method context.

QUESTION 4

What does the splat operator (*d) do in a method definition?

It forces the argument to be an integer.

It captures all remaining positional arguments into an array.

It marks the method as private.

It multiplies the following argument by itself.

QUESTION 5

Which keyword is used to transfer control from a method body to its associated block?

call

yield

next

delegate

✅ Correct!

yield executes the block associated with the method call.

❌ Incorrect

While Proc#call exists, yield is the primary mechanism for implicit block execution.

Case Study: The Dynamic Dispatcher

Architecting flexible method signatures

You are designing a notification system where a method notify(user, *messages, &callback) must process an unknown number of strings and then execute a custom formatting block provided by the developer.

How would you access the multiple messages passed after the user argument?

Solution:
By referencing the splat variable messages, which is automatically populated as an Array containing all additional positional arguments.

If the user provides a block like notify(u, m) { |msg| msg.upcase }, how do you trigger it inside the method?

Solution:
Use the yield keyword, or call the Proc object captured by the &callback parameter (e.g., callback.call(data)).

How can you ensure the method doesn't crash if no block is provided?

Solution:
Wrap the yield in a conditional check: yield if block_given?.