Evaluation order

ruby-talk
1

Lähettäjä: "David A. Black" <dblack@wobblini.net>
Aihe: Re: evaluation order

Hi --

>
> "Zehao" <zehao.chen@gmail.com> schrieb im Newsbeitrag
> news:1108274165.071278.164610@z14g2000cwz.googlegroups.com...
>> One interesting thing is when running the following codes
>>
>> File.open("testfile") |aFile| do
>> print a while a=aFile.gets
>> end
>>
>> one will get an error indicating a doesn't exist. This error can be
>> fixed by adding a line a="" before the print command.
>>
>> But logically speaking, "print a" should be interpreted after
>> "a=File.gets". Is this because the interpreter couldn't find the object
>> "a" when first scanning the second line?
>
> I suspect it's the same issue as with local variables: Ruby applies a certain
> heuristic to determine whether something is a local var or not. This
> heuristic is based on *syntactical* order of occurrence
>
>>> def foo
>>> print a
>>> a = 10
>>> end
> => nil
>>> foo
> NameError: undefined local variable or method `a' for main:Object
> from (irb):2:in `foo'
> from (irb):5

It's also fun to see what happens if you run this kind of thing twice:

irb(main):005:0> puts x if x = 1
NameError: undefined local variable or method `x' for main:Object
         from (irb):5
irb(main):006:0> puts x if x = 1
1

(For clarity I've deleted the warning about using '=' in conditional.
[Matz, can't we get rid of that warning?])

In general that's a useful warning... I'm assuming you may mean just
in a context where the statement modifier assigns to the variable?

David

E

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On Sun, 13 Feb 2005, Robert Klemme wrote: