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

ruby-talk
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 ?

···

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Posted via http://www.ruby-forum.com/\.

2

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"

···

2009/1/18 Raj Singh <neeraj.jsr@gmail.com>

>> 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 ?

3

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.

···

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

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 ?

--
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/