Question

Quine is a self reproducing code. For example if the code in groovy looks like:

def s = 20

When i run the above code, i should get the program statements as my outputs. So the above code should produce:

def s = 20 //as this is my input..

As I have seen in Groovy Console, i came to know groovy supports Quine :

s='s=\\\';s[0..1]+s[3]+s[0..1]+s[2]*6+s[3..-1]*2';s[0..1]+s[3]+s[0..1]+s[2]*6+s[3..-1]*2

But I don’t know how it works! Could any one say me, how the code in the above link works?

Thanks in advance!

Answer 1

The code in question is:

s='s=\\\';s[0..1]+s[3]+s[0..1]+s[2]*6+s[3..-1]*2';s[0..1]+s[3]+s[0..1]+s[2]*6+s[3..-1]*2

So, the left statement defines a string, then the right statement adds together different bits of the String:

If we add the following to print out what it’s doing:

println s[0..1]
println s[3]
println s[0..1]
println s[2] * 6
println s[3..-1] * 2

we get the output:

s=
'
s=
\\\
';s[0..1]+s[3]+s[0..1]+s[2]*6+s[3..-1]*2';s[0..1]+s[3]+s[0..1]+s[2]*6+s[3..-1]*2

And if you add all those strings together, you get the original program.