checking if a string matches a regexp - am I missing something?

[Rob Sanheim]

I figure that I must be missing something really obvious with this
question. But here goes:

I want to know if a string matches a regular expression. I don't care
where the match begins, I don't want a matchdata object, I don't want
to check for nil, I just want a boolean indicating if a string matches
a regexp. And I want this to be one method call. From what I can
tell, this is the closest I can get:

reg = /\w/
reg === "string" # close, but I want to send the message to the
string, not the other way around
("string" =~ reg) >= 0 # ugly
("string" =~ reg) != 0 # still ugly
"string".include? reg # this would seem to follow the ruby way, but it
throws a TypeError

If I'm not missing some other trick to do this, why doesn't include?
just allow regexp's like so many of the other (slice, index, scan,
etc) string methods?

- Rob

 

[James Edward Gray II]

I figure that I must be missing something really obvious with this
question. But here goes:

I want to know if a string matches a regular expression. I don't care
where the match begins, I don't want a matchdata object, I don't want
to check for nil, I just want a boolean indicating if a string matches
a regexp. And I want this to be one method call. From what I can
tell, this is the closest I can get:

("string" =~ reg) >= 0 # ugly

Just drop the noise:

"string" =~ reg # => int results are +true+ and nil is +false+

Hope that helps.

James Edward Gray II

 

[khaines]

I want to know if a string matches a regular expression. I don't care
where the match begins, I don't want a matchdata object, I don't want
to check for nil, I just want a boolean indicating if a string matches
a regexp. And I want this to be one method call. From what I can
tell, this is the closest I can get:

reg = /\w/
reg === "string" # close, but I want to send the message to the
string, not the other way around
("string" =~ reg) >= 0 # ugly
("string" =~ reg) != 0 # still ugly
"string".include? reg # this would seem to follow the ruby way, but it
throws a TypeError

What am I not understanding here?

"string" =~ reg


Kirk Haines

 

[Rob Sanheim]

Just drop the noise:

"string" =~ reg # => int results are +true+ and nil is +false+

Hope that helps.

True...but here is a cleaned up version of the place where I tried to do that:

def valid_query?
# query is a string accessor
if query_is_plain_text?
is_valid = valid_query_length? && (query =~ regex)
else
is_valid = query_is_url?
end
is_valid
end

So of course, when it was both a valid query and had a valid length,
it would return zero because it matched the start of the regexp. The
caller of the method wanted true or false only, not zero.

 

[James Edward Gray II]

True...but here is a cleaned up version of the place where I tried
to do that:

def valid_query?
# query is a string accessor
if query_is_plain_text?
is_valid = valid_query_length? && (query =~ regex)
else
is_valid = query_is_url?
end
is_valid
end

!!(query =~ regex)

James Edward Gray II

 

[Logan Capaldo]

True...but here is a cleaned up version of the place where I tried to do
that:

def valid_query?
# query is a string accessor
if query_is_plain_text?
is_valid = valid_query_length? && (query =~ regex)
else
is_valid = query_is_url?
end
is_valid
end

So of course, when it was both a valid query and had a valid length,
it would return zero because it matched the start of the regexp. The
caller of the method wanted true or false only, not zero.

The caller is poorly written then
To work around this:

!!is_valid # !! is like the to boolean operator
end

 

[William James]

True...but here is a cleaned up version of the place where I tried to do that:

def valid_query?
# query is a string accessor
if query_is_plain_text?
is_valid = valid_query_length? && (query =~ regex)
else
is_valid = query_is_url?
end
is_valid
end

So of course, when it was both a valid query and had a valid length,
it would return zero because it matched the start of the regexp. The
caller of the method wanted true or false only, not zero.

Who wrote a caller that wanted true or false only, and why?
What does the caller do when it receives 0?

irb(main):002:0> puts 'yeah' if true
yeah
=> nil
irb(main):003:0> puts 'yeah' if 0
yeah
=> nil
irb(main):004:0> puts 'yeah' if false
=> nil

If you actually have a caller written so mindlessly that it
only works with true or false:

!!(is_valid = valid_query_length? && (query =~ regex) )

 

[William James]

!!(is_valid = valid_query_length? && (query =~ regex) )

Make that

is_valid = !!(valid_query_length? && (query =~ regex) )

 

[Rob Sanheim]

Who wrote a caller that wanted true or false only, and why?
What does the caller do when it receives 0?

irb(main):002:0> puts 'yeah' if true
yeah
=> nil
irb(main):003:0> puts 'yeah' if 0
yeah
=> nil
irb(main):004:0> puts 'yeah' if false
=> nil

If you actually have a caller written so mindlessly that it
only works with true or false:

!!(is_valid = valid_query_length? && (query =~ regex) )

Well I guess I was mindless, then. =) I wrote a spec that was using
"should.be(true)" and "should.be(false)", which is using assert_same
underneath, so of course it was failing if it returned 0. So the easy
solution is to use should.equal instead of should.be. Thanks for the
double !! tip, though.

Now, about allowing regexp's for "include?" - doesn't that fit well
with the humane interface of String?

- Rob

 

[Wilson Bilkovich]

Well I guess I was mindless, then. =) I wrote a spec that was using
"should.be(true)" and "should.be(false)", which is using assert_same
underneath, so of course it was failing if it returned 0. So the easy
solution is to use should.equal instead of should.be. Thanks for the
double !! tip, though.

Now, about allowing regexp's for "include?" - doesn't that fit well
with the humane interface of String?

If you are using RSpec, you can simply say:
"blah".should =~ /ah/
or
"blah".should_not =~ /z/

If you want "include? with a Regexp" behavior, you can do:
if some_string[/some pattern/]

 

[Rob Sanheim]

Well I guess I was mindless, then. =) I wrote a spec that was using
"should.be(true)" and "should.be(false)", which is using assert_same
underneath, so of course it was failing if it returned 0. So the easy
solution is to use should.equal instead of should.be. Thanks for the
double !! tip, though.

Now, about allowing regexp's for "include?" - doesn't that fit well
with the humane interface of String?

If you are using RSpec, you can simply say:
"blah".should =~ /ah/
or
"blah".should_not =~ /z/

If you want "include? with a Regexp" behavior, you can do:
if some_string[/some pattern/]

Well the method under test (under spec?) wasn't dealing with regex.
It was just using a regex to figure out if something was valid, and
then checking some other things and returning what I thought would be
true or false. So thats why I couldn't use the should =~ methods, and
in the end really wanted should.equal (I'm using spec/unit, not
rspec).

- rob