comp.lang.ruby

Brian Candler

10/29/2008 12:37:00 PM

List Rb wrote:
> Hi. Is there a way to create a lambda that references local variables
> not yet defined ( with out pawing them to the prod) ?
>
> I.e.
> x = lambda {a+b}
> a = 1
> b = 2
> c = x.call

I don't know what "pawing them to the prod" means, but you can do

a, b = nil, nil
x = lambda {a+b}
a = 1
b = 2
c = x.call

This is because Ruby makes a parse-time decision as to whether 'a' is a
local variable or a method call. If no assignment to 'a' has been seen
earlier in the scope, then it is interpreted as a method call instead:
self.a()

Since this is done while the parse tree is built, prior to execution, it
doesn't make any difference whether the assignment is actually executed
or not. For example:

def x
"hello"
end

if false
x = 1
end

puts x # shows 'nil' since x is a local variable

This is necessary to have any sort of efficiency. Otherwise, a simple
statement like "b = a + 1" inside a loop would have to decide at
run-time, every time it is executed, whether 'a' is a local variable or
a method.
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