Undefined local var hash not trapped

Ruby
1

The following program:

K:\Analysis

TestUndefinedLocalVar_hash.rb

a = []
a << “xyz”
a << hash
a << undefined

crashes on line 8 (a << undefined) rather than on line 7 (which
apparently appends a reference to the undefined “hash” to the array.
What causes this mythical creation of “hash”? Is this behavior
defined anywhere?

If it matters, the following explains how I encountered this problem:

I have a program which had been using a local var named “hash”. Use
of that name caused no problem.
However, I decided I should change the value assigned to hash, so I
changed all references to it to “hash_string” … all but one. I
expected that after I made changes to the way hash_string was
computed, my program would fail when the reference to the now-
undefined hash was encountered. No such luck.

Thanks in Advance,
Richard

2

On Sat, Jan 1, 2011 at 4:25 PM, RichardOnRails
[email protected] wrote:

What causes this mythical creation of “hash”? Is this behavior
defined anywhere?

Uh, “mythical”?? Ruby does have docs, you know :slight_smile:

Hint: Object#hash would be a good place to look…

HTH,

3

On Jan 1, 7:24pm, RichardOnRails
[email protected] wrote:

crashes on line 8 (a << undefined) rather than on line 7 (which
expected that after I made changes to the way hash_string was
computed, my program would fail when the reference to the now-
undefined hash was encountered. No such luck.

Thanks in Advance,
Richard

HTH
That certainly helps in that it shows me what Ruby was “thinking”.

RubyDocs shows that lots of class have hash methods (maybe because
they all inherit from Object.) I listed a few “uses” below but have
adopted a new programming rule: don’t use Ruby method-names as local
variables.

Below are the few examples that seem pretty useless to me.

Best wishes,
Richard

a = []

a = “” # Can’t append hash to a string

a << hash
a << “xyz”

4

Object#Hash was a good indication.
in irb session, the IRB object #hash is executed when you type hash.

regarding strings, again, strings have a method << which is used for
appending. a<< hash will return in an error since hash returns a number
and
it is very large to be converted to a char…

On Sun, Jan 2, 2011 at 08:40, RichardOnRails <