eval/binding question

[Robert Klemme]

No. _code gets parsed on every call to local_eval.

If you want to avoid that you'll need a two step approach. But then the
var names are needed beforehand... Ok, I see the problem (finally)

Cheers

robert

I omitted the template name and the value as these are just special cases
of values with fixed names. But you get the picture. And there is no
reparsing needed.

def local_eval(_values, _code)
_val = nil
_bnd = binding
p local_variables
_values.each {|name, val| eval "#{name}=_val", _bnd}
p local_variables
eval _code, _bnd
end

local_eval( {:x=>1}, "puts x" )

["_values", "_code", "_val", "_bnd"]
["_values", "_code", "_val", "_bnd", "x"]
nil
=> nil

-- stefan

 

[Eric Hodel]

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Why did you lie???

I didn't bother to double-check first. My bad.

Thanks for the code, but I already knew this would also be a possible
solution. But probably less efficient than using instance variables,
though I have not checked that yet. Did you?

attr* methods are optimized for speed so you don't have all the
overhead of a regular method call, but I doubt this will be faster than
ivars.

An ivar implementation would be pretty easy too, use
instance_variable_set instead of send.

Here's how Ruby optimizes attr* methods:

$ parse_tree_show
class Example
attr_reader :x
def y() @y; end
end
[[:class,
:Example,
:Object,
[:defn, :x, [:ivar, x]],
[:defn, :y, [:scope, [:block, [:args], [:ivar, y]]]]]]

No scope setup is done for attr*.

--
Eric Hodel - (e-mail address removed) - http://segment7.net
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[samuel_x_winters_x]

+1

I have on a couple of occasions also been bit by this. It would be much
nicer (to the programmer, at any rate) for
code and eval "code"
to behave consistently with each other.

In particular, manipulating variable bindings is extremely difficult
without.

So I'd like to revive this request, if possible ...