Adding an argument to a proc

ruby-talk
1

is there a way to add an argument to a proc after its creation?

ex-

p = Proc.new { x + 5 }
px = Proc.new { |x| p.call(5) }

this won’t work

···

–
~transami

(") dobee dobee do…
\v/
^ ^

2

Tom Sawyer wrote:

is there a way to add an argument to a proc after its creation?

Don’t think so. Sounds like it would wreak a havoc of ambiguity on
variable scope

ex-

p = Proc.new { x + 5 }
px = Proc.new { |x| p.call(5) }

this won’t work

You could perhaps be nasty and run eval on the binding of the block and
setting the scope local variable explicitly, before calling the proc.

x = nil # Has to exist in scope of block definition p1 = Proc.new { x + 5 }

Define a wrapper Proc that sets the x to a number

p2 = Proc.new {|y_uNiQuE_VarName|
eval “old_x_uNiQuE_VarName = x”, p1
eval “x=#{y_uNiQuE_VarName}”, p1 # naive version
result = p1.call
eval “x=old_x_uNiQuE_VarName”, p1
result
}

Less naive version that should work with any object

p3 = Proc.new {|y_uNiQuE_VarName|
eval “old_x_uNiQuE_VarName = x”, p1
eval “x=ObjectSpace._id2ref(#{y_uNiQuE_VarName.id})”, p1 # less naive
result = p1.call
eval “x=old_x_uNiQuE_VarName”, p1
result
}

puts p2.call(5) #=> 10
puts p3.call(15) #)=> 20

puts “Dang!” if x != nil

···

–
([ Kent Dahl ]/)_ ~ [ http://www.stud.ntnu.no/~kentda/ ]/~
))_student/(( _d L b_/ NTNU - graduate engineering - 4. year )
( __õ|õ// ) )Industrial economics and technological management(
_/ö____/ (_engineering.discipline=Computer::Technology)

3

Kent,

yuk, that is nasty! neat hack though. i’ll see if i can just make do
with having to have the argument - its only a minor inconvience.

have any ideas about my super in proc post? that one is kind of vital. i
don’t know what i’ll do if i can’t figure that one out.

thanks!
~tom

···

On Mon, 2002-07-22 at 04:24, Kent Dahl wrote:

Tom Sawyer wrote:

is there a way to add an argument to a proc after its creation?

Don’t think so. Sounds like it would wreak a havoc of ambiguity on
variable scope

ex-

p = Proc.new { x + 5 }
px = Proc.new { |x| p.call(5) }

this won’t work

You could perhaps be nasty and run eval on the binding of the block and
setting the scope local variable explicitly, before calling the proc.

x = nil # Has to exist in scope of block definition p1 = Proc.new { x + 5 }

Define a wrapper Proc that sets the x to a number

p2 = Proc.new {|y_uNiQuE_VarName|
eval “old_x_uNiQuE_VarName = x”, p1
eval “x=#{y_uNiQuE_VarName}”, p1 # naive version
result = p1.call
eval “x=old_x_uNiQuE_VarName”, p1
result
}

Less naive version that should work with any object

p3 = Proc.new {|y_uNiQuE_VarName|
eval “old_x_uNiQuE_VarName = x”, p1
eval “x=ObjectSpace._id2ref(#{y_uNiQuE_VarName.id})”, p1 # less naive
result = p1.call
eval “x=old_x_uNiQuE_VarName”, p1
result
}

puts p2.call(5) #=> 10
puts p3.call(15) #)=> 20

puts “Dang!” if x != nil

–
([ Kent Dahl ]/)_ ~ [ http://www.stud.ntnu.no/~kentda/ ]/~
))_student/(( _d L b_/ NTNU - graduate engineering - 4. year )
( __õ|õ// ) )Industrial economics and technological management(
_/ö____/ (_engineering.discipline=Computer::Technology)

–
~transami

(") dobee dobee do…
\v/
^ ^

4

Kent Dahl wrote:

p2 = Proc.new {|y_uNiQuE_VarName|

Ops. You don’t have to go nuts on the y like this. I was trying
something and forgot to change the y name back.

···

–
([ Kent Dahl ]/)_ ~ [ http://www.stud.ntnu.no/~kentda/ ]/~
))_student/(( _d L b_/ NTNU - graduate engineering - 4. year )
( __õ|õ// ) )Industrial economics and technological management(
_/ö____/ (_engineering.discipline=Computer::Technology)