Require vs Load in Ruby: Key Differences and Usage

require loads a file once and caches it, preventing multiple loads, while load reloads the file every time it is called. Use require for libraries and load when you need to reload code dynamically.

Quick Comparison

This table summarizes the main differences between require and load in Ruby.

Factor	require	load
File loading frequency	Loads file only once	Loads file every time called
File extension needed	Optional (.rb assumed)	Must specify full filename including extension
Caching behavior	Caches loaded files	Does not cache, reloads always
Use case	Loading libraries or gems	Reloading code dynamically during runtime
Return value	true if file loaded, false if already loaded	true if successful
Performance	Faster after first load due to caching	Slower due to repeated loading

Key Differences

require is designed to load external files or libraries only once during the program execution. It keeps track of loaded files and skips reloading them if called again, which improves performance and avoids duplicate definitions.

On the other hand, load reads and processes the specified file every time it is called, regardless of previous loads. This is useful when you want to reload code changes without restarting the program, such as during development or dynamic scripting.

Another difference is that require allows omitting the file extension (usually .rb), while load requires the full filename including extension. Also, require returns false if the file was already loaded, whereas load always returns true if successful.

Code Comparison

Here is an example showing how require loads a file only once.

ruby

puts "Before require"
require './example.rb'
require './example.rb'
puts "After require"

Output

Before require
Hello from example.rb
After require

Load Equivalent

This example shows how load reloads the same file every time it is called.

ruby

puts "Before load"
load './example.rb'
load './example.rb'
puts "After load"

Output

Before load
Hello from example.rb
Hello from example.rb
After load

When to Use Which

Choose require when you want to load libraries or files once to avoid duplication and improve performance. It is the standard way to include code in Ruby programs.

Choose load when you need to reload a file multiple times during runtime, such as when testing changes without restarting the program or dynamically updating code.

Key Takeaways

require loads files once and caches them to prevent duplicates.

load reloads files every time it is called, useful for dynamic code updates.

require can omit file extensions; load requires full filename.

Use require for libraries and load for reloading code during runtime.

require returns false if file already loaded; load always returns true.