weird behaviour

[lopex]

Hello

Ruby complains when it tries to parse:

"" + "".to_s +""

but the following are correct:

"" + "".to_s + ""
"" + "" +""

Is it because there is no +@ operator defined for the String class ?
If so, why the latter is parsed silently ?

Marcin Mielzynski

 

[ts]

l> Is it because there is no +@ operator defined for the String class ?

no, this is this case

svg% ruby -e '"".to_s +""'
-e:1: undefined method `+@' for "":String (NoMethodError)
svg%

l> If so, why the latter is parsed silently ?

because with '"" + "".to_s +""' ruby has seen an identifier and it don't
expect +"" at this step


Guy Decoux

 

[Robert Klemme]

l> Is it because there is no +@ operator defined for the String class ?

no, this is this case

svg% ruby -e '"".to_s +""'
-e:1: undefined method `+@' for "":String (NoMethodError)
svg%

l> If so, why the latter is parsed silently ?

because with '"" + "".to_s +""' ruby has seen an identifier and it don't
expect +"" at this step

Maybe Ruby tries to parse +"" as unary plus (i.e. number sign) and then
fails on the "" part.

robert

 

[ts]

R> Maybe Ruby tries to parse +"" as unary plus (i.e. number sign) and then
R> fails on the "" part.

run it with -w


Guy Decoux

 

[Robert Klemme]

R> Maybe Ruby tries to parse +"" as unary plus (i.e. number sign) and then
R> fails on the "" part.

run it with -w

Good point. I guess "-e:1: undefined method `+@' for "":String
(NoMethodError)" means that the unary plus is not defined for String.
Correct?

Regards

robert

 

[ts]

R> Good point. I guess "-e:1: undefined method `+@' for "":String
R> (NoMethodError)" means that the unary plus is not defined for String.
R> Correct?

yes,


Guy Decoux

 

[Dave Burt]

So
"".to_s +""
means
"".to_s(+"")

and adding parens like so:
"".to_s() +""
would correct the problem.

 

[ts]

D> So
D> "".to_s +""
D> means
D> "".to_s(+"")

it's a little more complex

"".to_s +""

is interpreted as

"".to_s(+"") # unary plus

and

"".to_s+""

is interpreted as

"".to_s + "" # addition

*but*

"" + "".to_s +""

is interpreted as

("" + "".to_s) +""

this is why ruby give an error, it has an unary plus which don't give a
valid expression

D> and adding parens like so:
D> "".to_s() +""
D> would correct the problem.

yes, because with

"" + "".to_s() +""

it's interpreted as

("" + "".to_s()) + ""

the second `+' is seen as the addition not the unary plus

like in this case

"" + "".to_s+""




Guy Decoux