Send for calling methods dynamically in Ruby - Time & Space Complexity

Time Complexity: Send for calling methods dynamically

O(n)

Understanding Time Complexity

When we use send in Ruby to call methods dynamically, it is important to understand how this affects the time it takes to run the program.

We want to know how the number of method calls grows as we call more methods dynamically.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class Greeter
  def hello
    "Hello!"
  end

  def goodbye
    "Goodbye!"
  end
end

g = Greeter.new
methods = [:hello, :goodbye]
methods.each { |m| puts g.send(m) }

This code calls methods dynamically on an object using send inside a loop.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Calling send to invoke a method dynamically.
• How many times: Once for each method symbol in the methods array.

How Execution Grows With Input

Each method call happens once per item in the list of method names.

Input Size (n)	Approx. Operations
10	10 method calls via send
100	100 method calls via send
1000	1000 method calls via send

Pattern observation: The number of dynamic calls grows directly with the number of methods to call.

Final Time Complexity

Time Complexity: O(n)

This means the time to run grows linearly with the number of methods called dynamically.

Common Mistake

[X] Wrong: "Using send makes the code slower in a way that changes the overall time complexity."

[OK] Correct: Calling methods dynamically with send adds a small fixed overhead per call but does not change how the total time grows with the number of calls.

Interview Connect

Understanding how dynamic method calls scale helps you explain your code's performance clearly and confidently in real projects or interviews.

Self-Check

What if we replaced the array of method names with a nested loop calling send multiple times per method? How would the time complexity change?

Practice

1. What does the Ruby method send do when used like obj.send(:method_name)?

easy

A. Calls the method named method_name on obj dynamically.

B. Creates a new method called method_name on obj.

C. Deletes the method named method_name from obj.

D. Returns the name of the method as a string.

Solution

1. Step 1: Understand send usage

   The send method calls a method on an object using the method's name given as a symbol or string.

2. Step 2: Analyze the example obj.send(:method_name)

   This calls the method named method_name on obj dynamically at runtime.

3. Final Answer:

   Calls the method named method_name on obj dynamically. -> Option A

4. Quick Check:

   send calls methods dynamically [OK]

Hint: Remember: send calls methods by name on objects [OK]

Common Mistakes:

• Thinking send creates or deletes methods
• Confusing send with method name retrieval
• Assuming send returns method names as strings

2. Which of the following is the correct syntax to call a method named greet on object user using send?

easy

A. user.send(greet)

B. user.send('greet')()

C. user.send['greet']

D. user.send(:greet)

Solution

1. Step 1: Recall send syntax

   The method name should be passed as a symbol or string without parentheses after send.

2. Step 2: Check each option

   user.send(greet) misses quotes or symbol, causing error. user.send(:greet) correctly uses a symbol :greet. user.send('greet')() wrongly adds parentheses after send call. user.send['greet'] uses incorrect bracket syntax.

3. Final Answer:

   user.send(:greet) -> Option D

4. Quick Check:

   Use symbol for method name in send [OK]

Hint: Use colon before method name symbol in send [OK]

Common Mistakes:

• Passing method name without quotes or colon
• Adding parentheses after send call
• Using brackets [] instead of parentheses ()

3. What is the output of this Ruby code?

class Person
  def greet(name)
    "Hello, #{name}!"
  end
end

p = Person.new
puts p.send(:greet, "Alice")

medium

A. Hello, Alice!

B. greet

C. NoMethodError

D. Hello, name!

Solution

1. Step 1: Understand the method call with send

   The send method calls greet on p with argument "Alice".

2. Step 2: Evaluate the method output

   The greet method returns "Hello, Alice!" which is printed by puts.

3. Final Answer:

   Hello, Alice! -> Option A

4. Quick Check:

   send calls greet with argument "Alice" [OK]

Hint: send passes arguments after method name [OK]

Common Mistakes:

• Expecting method name string as output
• Confusing argument passing with no arguments
• Thinking send returns method object

4. Identify the error in this Ruby code snippet:

class Calculator
  def add(a, b)
    a + b
  end
end

calc = Calculator.new
calc.send(:add, 5)

medium

A. send cannot be used with arguments

B. Method add does not exist

C. Missing second argument for method add

D. Syntax error in method definition

Solution

1. Step 1: Check method definition

   The method add requires two arguments: a and b.

2. Step 2: Analyze the send call

   The send call provides only one argument (5), missing the second argument.

3. Final Answer:

   Missing second argument for method add -> Option C

4. Quick Check:

   Method arguments must match when using send [OK]

Hint: Match method arguments count when using send [OK]

Common Mistakes:

• Passing fewer arguments than method requires
• Assuming send works without correct arguments
• Thinking send changes method signature

5. You want to call different arithmetic methods (add, subtract, multiply) on a Calculator object dynamically based on user input stored in operation. Which Ruby code correctly uses send to achieve this?

class Calculator
  def add(a, b); a + b; end
  def subtract(a, b); a - b; end
  def multiply(a, b); a * b; end
end

calc = Calculator.new
operation = :multiply
# Fill in the blank below to call the method dynamically
result = ???
puts result

hard

A. calc.send(:operation, 4, 5)

B. calc.send(operation, 4, 5)

C. calc.send('operation', 4, 5)

D. calc.send(operation())

Solution

1. Step 1: Understand dynamic method calling

   The variable operation holds the symbol of the method to call.

2. Step 2: Use send with variable method name and arguments

   Passing operation as the first argument to send calls the correct method with arguments 4 and 5.

3. Final Answer:

   calc.send(operation, 4, 5) -> Option B

4. Quick Check:

   send uses variable method names with arguments [OK]

Hint: Pass method name variable and args directly to send [OK]

Common Mistakes:

• Passing method name as string literal instead of variable
• Adding parentheses after variable name incorrectly
• Using symbol literal instead of variable for method name