From: dale.quigg@...
Date: 2006-12-05T05:20:08+09:00
Subject: Re: How to make "generic" YAML calls?

Gregory Seidman wrote:
> On Fri, Dec 01, 2006 at 08:45:05AM +0900, dale.quigg@aspentech.com wrote:
> } dale.quigg@aspentech.com wrote:
> } <snip>
> } > However, I want to write a class where I pass something like
> } >   '["This"]["Thing"]'
> } > or
> } >   '["That"]["Thing"]'
> } > and then make a call like;
> } >   puts LocalTree@YamlLocation
> } > but I can't figure out how to make this work.
> }
> } Found it, sorry to bother.
> } yaml_vari = '["This"]["Thing"]'
> } puts eval("LocalTree" + yaml_vari)
>
> In general, eval should be avoided. Try this:
>
> def retrieve(*path)
>   path.inject(LocalTree) { |obj,key| obj[key] }
> end
>
> Call it as retrieve('This', 'Thing'), for your example.
>
> --Greg

Thank you Greg.

I applied your suggestion to my application and it works.

In trying to further understand how .inject works, I looked in the
pickaxe book and found that this would cause (possibly many)
intermediate values to be retrieved (depending on YAML configuration)
while only the last value is returned.  I ran a quick benchmark and the
.inject code was about 28% slower than using eval in my application.

This "slowdown" doesn't really matter, but I was thinking that  perhaps
it could be significant if the YAML file size increased.  But, if this
happens, perhaps I shouldn't be using YAML to store the data.  :-)

Do you know of a way to reduce the number of evaluations that occur
when using inject?

Also, can you give a quick pointer as to why eval should be avoided?

Thanks again for your reply.
Dale