Re-naming a block

ruby-talk
1

Hi all.

I'm writing a method which takes a block and returns a lambda which will
execute that block when called. Here's the code:

def foo &block
  Proc.new { yield }
end

a = foo { 3 }
puts a

This returns something like #<Proc:0x2a50b08@scratch2.rb:2 (lambda)>. That's
all well and good, but what I'd really like is for that line number to show
up as 5, since that's where the block is actually defined. So I try this:

def foo &block
  a = Proc.new { yield }
  def a.to_s
    block.to_s
  end
  a
end

a = foo { 3 }
puts a

But here, ruby tells me that 'block' is undefined inside a's to_s. It's
clearly not creating the closure I'd hoped for. I've played around with a
few variations, but can't seem to get it to do what I want. Suggestions?

2

def creates a new scope, not a closure. Try define_method:

def foo &block
  a = Proc.new {yield}
  class << a; self; end.send(:define_method, :to_s) {block.to_s}
  a
end

Jesus.

···

On Sat, Oct 23, 2010 at 7:43 PM, Andrew Wagner <wagner.andrew@gmail.com> wrote:

Hi all.

I'm writing a method which takes a block and returns a lambda which will
execute that block when called. Here's the code:

def foo &block
Proc.new { yield }
end

a = foo { 3 }
puts a

This returns something like #<Proc:0x2a50b08@scratch2.rb:2 (lambda)>. That's
all well and good, but what I'd really like is for that line number to show
up as 5, since that's where the block is actually defined. So I try this:

def foo &block
a = Proc.new { yield }
def a.to_s
block.to_s
end
a
end

a = foo { 3 }
puts a

But here, ruby tells me that 'block' is undefined inside a's to_s. It's
clearly not creating the closure I'd hoped for. I've played around with a
few variations, but can't seem to get it to do what I want. Suggestions?

3

Well maybe the answer is to create a proc with the right line number
from the beginning:

def foo &block
Proc.new(&block)
end

a = foo { 3 }
puts a

puts a.call

#<Proc:0x000000010012e688@untitled:5>
3

···

On Sat, Oct 23, 2010 at 1:43 PM, Andrew Wagner <wagner.andrew@gmail.com> wrote:

def foo &block
Proc.new { yield }
end

a = foo { 3 }
puts a

--
Rick DeNatale

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