In Ruby, if you assign a function to a variable, why does it automatically run?

Question

Using the code below:

variable = puts "hello world".upcase

Why does Ruby automatically puts Hello world in upcase, without the variable first being invoked? I understand that you are setting the function to the variable, and if that variable is called it will return the return value (in this case, nil), but why is it that Ruby runs the method puts "hello world".upcasealmost without permission (have not called it, merely assigned to a variable)?

You are not assigning function to variable. You are assigning return value of function to variable so the function runs first so you get the value for assignment. — jan.zikan
– jan.zikan, Commented Oct 31, 2016 at 19:22
Ruby doesn't have pure first-class functions like Python or JavaScript. In Python, you have to call a function -- foo is a reference to the function object foo, and foo() is a call to that function. In Ruby, foo is a call to the function -- other syntax is needed to get a Method object. — Linuxios
– Linuxios, Commented Oct 31, 2016 at 19:30

Ursus · Accepted Answer · 2016-10-31 19:22:51Z

14

You are not assigning a function to a variable.

This is the same as

variable = (puts("hello world".upcase))

It needs to execute puts to assign the returned value to the variable variable (lol).

This is a way to assign a method to a variable.

puts_method = method(:puts)

answered Oct 31, 2016 at 19:22

Ursus

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4 Comments

developer098 Over a year ago

I've tried to put in method = puts(:hello), but it like the other variable example just runs similarly without permission. Could you provide an example using puts "hello world" where it would store the method within the variable without running it?

Ursus Over a year ago

In ruby there are these callable objects. Something like puts_hello_word = lambda { puts "hello world" }

Ursus Over a year ago

and call it with puts_hello_word.call

developer098 Over a year ago

Ok, I will look into that. Thank you for your time spent answering the question @Ursus.

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