Regex#=== with non-string argument

ruby-talk
1

I’m surprised:

x = 1

case x
when 5; puts "5"
when 42; puts "42"
when /abc/; puts "matches /abc/"
when “xyz”; puts "xyz"
end

This is a TypeError. Is there any good reason why?

I think it would make sense for Regex#=== (if not Regex#=~) to return
false for non-Strings. Otherwise, this kind of case statement has to be
broken into an ‘if…else…end’ and two ‘case…end’ statements.

Anyway this workaround is no good for me because, instead of a case
statement, I have a list of given objects which respond to :===. I guess
I could test for Regex, but that’s not very elegant. Also, I can’t just
rescue TypeError, because I can’t be sure that a given (user-supplied)
object uses TypeError in this way (and maybe the TypeError is a
programming error inside the user’s #=== implementation).

The same goes for Range#=== .

2

x = 1
puts case
when x == 5; “5”
when x == 42; “42”
when /abc/ =~ x.to_s; “matches /abc/”
when “xyz” == x.to_s; “xyz”
else “none”
end

case without a statement matches any expression that evaluates to a
non-false, non-nil argument

Hope that’s what you want

  • Greg.
···

On Wed, 18 Dec 2002, Joel VanderWerf wrote:

x = 1

case x
when 5; puts “5”
when 42; puts “42”
when /abc/; puts “matches /abc/”
when “xyz”; puts “xyz”
end

–
Greg Millam
walker at deafcode.com

3

Hi,

···

In message “Regex#=== with non-string argument” on 02/12/18, Joel VanderWerf vjoel@PATH.Berkeley.EDU writes:

I’m surprised:

x = 1

case x
when 5; puts “5”
when 42; puts “42”
when /abc/; puts “matches /abc/”
when “xyz”; puts “xyz”
end

This is a TypeError. Is there any good reason why?

No. I will fix this in the development version. And I confirmed no
other === method raise TypeError exception.

						matz.
4

Greg Millam wrote:

x = 1

case x
when 5; puts “5”
when 42; puts “42”
when /abc/; puts “matches /abc/”
when “xyz”; puts “xyz”
end

x = 1
puts case
when x == 5; “5”
when x == 42; “42”
when /abc/ =~ x.to_s; “matches /abc/”
when “xyz” == x.to_s; “xyz”
else “none”
end

case without a statement matches any expression that evaluates to a
non-false, non-nil argument

Hope that’s what you want

  • Greg.

Thanks, but no. I happily discovered that fact a few days ago, but my
real interest here is not case but a list of objects that respond to
:=== (and that’s all I know about them), and a piece of code that
iterates over them looking for a match with a fixed object. I don’t know
whether that fixed object has a #to_s method, or what its semantics are,
so I can’t use it. Anyway, I don’t want to lose the distinction between
Object and “Object”.

···

On Wed, 18 Dec 2002, Joel VanderWerf wrote:

5

Yukihiro Matsumoto wrote:

Hi,

I’m surprised:

x = 1

case x
when 5; puts “5”
when 42; puts “42”
when /abc/; puts “matches /abc/”
when “xyz”; puts “xyz”
end

This is a TypeError. Is there any good reason why?

No. I will fix this in the development version. And I confirmed no
other === method raise TypeError exception.

  					matz.

Great. By “other”, I assume you mean besides Regex and Range…
Thanks!

···

In message “Regex#=== with non-string argument” > on 02/12/18, Joel VanderWerf vjoel@PATH.Berkeley.EDU writes: