Why can't I define vars in caller's binding using eval?

Ruby
1

In other words, why can’t I do this?

def f(b)
eval(“x = 10”, b)
end

f(binding)
puts “x = #{x}”

Is there any way to make that code work (besides obviously setting x
to something before calling f).

Thanks.

2

Christopher J. Bottaro wrote:

In other words, why can’t I do this?

def f(b)
eval(“x = 10”, b)
end

f(binding)
puts “x = #{x}”

Is there any way to make that code work (besides obviously setting x
to something before calling f).

Thanks.

Worked for me.

Dios:~ andrewmitchell$ irb

def f(b)
eval(“x=10”, b)
end
=> nil

f(binding)
=> 10

puts “x = #{x}”
x = 10
=> nil

3

2008/5/23 Andrew M. [email protected]:

Is there any way to make that code work (besides obviously setting x
=> nil

f(binding)
=> 10
puts “x = #{x}”
x = 10
=> nil

But it works only in irb.

Regards,

Park H.

4

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As far as i know, this is because local variables have a lexical scope.

In my experience, the parser treats everything that was not mentioned
as a
local variable before a method call and the runtime doesn’t check
whether
it is a variable.

This also explains why IRB works differently, as every statement is
compiled
as a single statement.

Because of this, it is also impossible to assume the existance of
local variables
when executing a Proc in a certain context. (without considering hefty
AST-Hacking
with ruby2ruby).

Regards,
Florian G.

On May 23, 2008, at 11:13 AM, Heesob P. wrote:

end

Park H.

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