Why eval is not failing in the third case ( c3)

Ruby
1

c1 = ‘hello’
eval c1
NameError: undefined local variable or method `hello’ for main:Object

c2 = ‘hello #{hi}’
=> “hello #{hi}”

eval c2
NameError: undefined local variable or method `hello’ for main:Object

c3 = ‘#{hi} hello’
=> “#{hi} hello”

eval c3
=> nil

My question is why the eval of c3 is returning nil. It should fail
saying that undefined local variable just as it did in the case of c2 ?

2

2009/1/18 Raj S. [email protected]

=> “#{hi} hello”

eval c3
=> nil

My question is why the eval of c3 is returning nil. It should fail
saying that undefined local variable just as it did in the case of c2 ?

It’s evaluated as a comment:
#hi hello
If you want #{hi} to be replaced by the content of the variable hi, you
should use double quotes:
c4 = “#{hi} hello”

3

On Sun, 18 Jan 2009 16:35:31 -0500, Raj S. wrote:

=> “#{hi} hello”

eval c3
=> nil

My question is why the eval of c3 is returning nil. It should fail
saying that undefined local variable just as it did in the case of c2 ?

In the second and third cases, everything after (and including) the # is
interpreted as a comment. Thus, you’re executing

hello
hello #{hi}
#{hi} hello

In case 1, hello is a undefined method, so a NameError is raised
In case 2, hello comes before the comment, so it gets executed (with no
arguments). A NameError is raised because it’s an undefined method.
In case 3, hello is part of the comment. Nothing gets executed, so no
NameError is raised.