From: "Thomas B." <tpreal@...>
Date: 2008-10-13T06:20:36+09:00
Subject: Re: why the object doesn't respond to its method?

Li Chen wrote:
> Hi Thomas,
> 
> I find the method "Visible" but not"Visible=" here but the 
> respond_to?("Visible") still return false. I don't know how to explain 
> it.

This is correct. As it has been said, the respond_to? doesn't work with 
ole methods as they are served by metod_missing, which means that there 
are no such methods defined for this object. A sample to illustrate 
this:

class K
  def method_missing(m)
    puts "Inside qwe" if m==:qwe
  end
end
k=K::new
k.respond_to? :qwe #=> false
k.qwe ## prints: Inside qwe

So you are not able to check if there is an ole method using 
respond_to?. I hoped I stated it clearly in the above post, but 
apparently not.

Now the other problem: when you write excel.Visible=true, you call the 
method Visible=, but, as already stated, respond_to? :Visible= will not 
detect the presence of this method. You have to look for this method in 
the ole_methods table.

In general, ole methods are divided into two groups - setters (those 
that you call with = at the end, like Visible=) and other methods (those 
without =, like when you call excel.Visible (it returns the current 
status) or any other of similar methods. But in the ole_methods table, 
they are all reported without the =, that's why you see two elements 
Visible in the table returned by excel.ole_methods. To distinguish 
between them, it's better to look up the method you are looking for in 
the specific ole methods table, so: you look for setters inside 
excel.ole_put_methods, and for other methods inside 
excel.ole_get_methods. So, to check if there is a method called Visible 
(without =, the getter), you run this code:
excel.ole_get_methods.find{|m| m.name=="Visible"}
It returns nil if the method is not present and calling excel.Visible 
will raise an error, and a non-nil value if the ole method is present.
But if you want to check if there is a setter, that is, a method named 
Visible=, then you have to look it up in the other table:
excel.ole_put_methods.find{|m| m.name=="Visible"}
Again, nil means no method, non-nil means that method Visible= is 
present for the object. Note that in the last code line there is no 
"Visible=", but "Visible", and this is because ole setters in the ole 
methods table do not have the = in name, even though they are setters. 
And that's the very reason why we must look up setters and getters in 
two distinct tables.

If you want, you can add a method like ole_respond_to? to the class 
WIN32OLE, like this:

class WIN32OLE
  def ole_respond_to?(m)
    m=m.to_s
    if m[-1]==?=
      m=m[0...-1]
      table=ole_put_methods
    else
      table=ole_get_methods
    end
    !!table.find{|om| om.to_s==m}
  end
end

excel.ole_respond_to? :Visible= #=> true

Not tested carefully, so rather don't use it unless you can understand 
it.

Hope this helps.

TPR.
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