Method_missing for catch-all in Ruby - Time & Space Complexity

Time Complexity: Method_missing for catch-all

O(n)

Understanding Time Complexity

We want to understand how the time it takes to run a method_missing catch-all grows as we call different methods.

Specifically, how does the program behave when it handles unknown method calls?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class CatchAll
  def method_missing(name, *args)
    "You called: #{name} with #{args.length} arguments"
  end
end

obj = CatchAll.new
obj.any_method(1, 2, 3)

This code catches any unknown method call and returns a message including the method name and argument count.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The method_missing is called once per unknown method call.
• How many times: Once per unknown method call; no loops or recursion inside method_missing.

How Execution Grows With Input

Each unknown method call triggers method_missing once, doing a simple string operation.

Input Size (n)	Approx. Operations
10 unknown calls	10 simple string operations
100 unknown calls	100 simple string operations
1000 unknown calls	1000 simple string operations

Pattern observation: The work grows directly with the number of unknown method calls, each handled quickly.

Final Time Complexity

Time Complexity: O(n)

This means the time grows linearly with the number of unknown method calls made.

Common Mistake

[X] Wrong: "method_missing runs once and handles all unknown calls at once."

[OK] Correct: method_missing runs separately for each unknown call, so time adds up with each call.

Interview Connect

Understanding how method_missing works helps you reason about dynamic method handling and its cost in real programs.

Self-Check

"What if method_missing called another method inside that loops over arguments? How would the time complexity change?"