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comp.lang.ruby

optparse: on() vs on_tail

James Gray

3/3/2005 2:45:00 AM

Can someone tell me the difference between the on() and on_tail()
methods of OptionParser. I can't seem to figure it out. Thanks.

James Edward Gray II
4 Answers

Eric Hodel

3/3/2005 2:54:00 AM

0

On 02 Mar 2005, at 18:45, James Edward Gray II wrote:

> Can someone tell me the difference between the on() and on_tail()
> methods of OptionParser. I can't seem to figure it out. Thanks.

from optparse.rb:

=begin
--- OptionParser#on(*opts) [{...}]
--- OptionParser#def_option(*opts) [{...}]
--- OptionParser#on_head(*opts) [{...}]---
OptionParser#def_head_option(*opts) [{...}]
--- OptionParser#on_tail(*opts) [{...}]
--- OptionParser#def_tail_option(*opts) [{...}]
Defines option switch and handler. (({on_head})),
(({def_head_option}))
and (({on_tail})), (({def_tail_option})) put the switch at head
and tail of summary, respectively.

cf. ((<OptionParser#switch>)).
=end #'#"#`#

If you read down from there, on_tail/on add things to the end, of the
args list summary while on_head adds them to the front.

It looks like on_tail only exists to make things pretty.

--
Eric Hodel - drbrain@segment7.net - http://se...
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James Gray

3/3/2005 3:01:00 AM

0

On Mar 2, 2005, at 8:54 PM, Eric Hodel wrote:

> If you read down from there, on_tail/on add things to the end, of the
> args list summary while on_head adds them to the front.
>
> It looks like on_tail only exists to make things pretty.

Thanks much.

James Edward Gray II

James Gray

3/3/2005 3:22:00 AM

0

On Mar 2, 2005, at 8:54 PM, Eric Hodel wrote:

> If you read down from there, on_tail/on add things to the end, of the
> args list summary while on_head adds them to the front.

While we're on the subject, if you just use on(), are options added to
the summary in order? Thanks again.

James Edward Gray II

Thomas Kirchner

3/3/2005 1:12:00 PM

0

* On Mar 3 12:22, James Edward Gray II (ruby-talk@ruby-lang.org) wrote:
> While we're on the subject, if you just use on(), are options added to
> the summary in order? Thanks again.

Yeah, they're added in the order that you declare them. on_head is useful
for general, common options that most everyone needs, so that they appear
first. on() adds everything to the middle in order. on_tail is good for
generic options like --help or --version that aren't vital, but should be
there. Or at least that's how I use it :)

There's some decent documentation and a good example here:
http://www.ruby-doc.org/stdlib/libdoc/optparse/rdoc/classes/OptionP...
Hope that helps.
Tom