I’m working my way through the second edition of the pickaxe and have
encountered an example that doesn’t work as I’d expected.
while line = gets
puts line.downcase
end
That code made sense… it was then simplified to:
puts line.downcase while line = gets
This doesn’t work the same, however. I get:
02.07.rb:1: undefined local variable or method `line’ for main:Object
(NameError)
The odd part (to me) is that the error isn’t spit out until after I’ve
entered a line. In which order does the interpreter do it’s job? Even
more perplexing is:
line = ‘This will never be seen…’
puts line.downcase while line = gets
Defining line solves the issue. So, it seems to me, gets is executed
but something is erroring before the assignment to line… ? Any help
in understanding would be greatly appreciated!
“D” == Dustin McCormick [email protected] writes:
D> while line = gets
When ruby see the assignement =' it will think that
line’ is a
variable.
Then when it parse `gets’ and because it’s the first time than it seen
it,
it will resolved as a method call.
D> puts line.downcase
at this step, ruby now that `line’ make reference to a variable
D> end
D> puts line.downcase while line = gets
When it parse this line : it find `line’ and this is the first time
that
it seen it and it’s not an assignement. For ruby it’s a method call
When it parse ‘line =’, this time line will be referenced as a variable
You can see it with something like this
moulon% cat b.rb
#!/usr/bin/ruby
def line
“ABC”
end
puts line.downcase while (line = gets).chomp != ‘123’
puts line
moulon%
moulon% ./b.rb
XYZ
abc
ERT
abc
123
123
moulon%
The first reference is for the method #line, the 2 others for the
variable
`line’
D> 02.07.rb:1: undefined local variable or method `line’ for main:Object
D> (NameError)
Here ruby is trying to say :
-
at compile time, it has not found a variable line when it parsed
this
part of the source and it has resolved `line’ as a method call
-
at runtime, it has not found a method #line
D> line = ‘This will never be seen…’
D> puts line.downcase while line = gets
Here ruby has seen an affection before the while and it know that
`line’
make reference to a variable
Guy Decoux