method with yield via send

[Csaba Henk]

Hi!

The following, of course, works fine:

class C
def foo
yield * 2
end
end

C.new.foo {5}
=> 10

but if I do:

foop = proc { yield * 2 }

then

foop.call {5}

doesn't pass the block to yield, and if I define c as:

c = Class.new
c.senddefine_method,:foo,foop)

then

c.new.foo {5}

neither works.

Is there a way to define a method like the foo of C in the
c.senddefine_method,...) way?

Thanks,
--
Csaba

"There's more to life, than books, you know but not much more..."
[The Smiths]
***
If you want to send me a mail, see it in the mailto link at
http://www.renyi.hu/~ekho/egyelore.html

 

[Mark Hubbart]

Hi,

The main problem here, I think, is the context of the blocks you are
passing. They are bound into the current context. When you say 'foop =
proc { yield * 2 }', the yield is for the current context, where there
is no block to yield to.

Here's an example of the strange way contexts work when you define
methods using blocks/procs:

# set some variables
foo, bar, baz = 23, 42, 93
==>[23, 42, 93]
# create a class, define a method which shows the values of foobarbaz
c = Class.new
==>#<Class:0x713c4>
c.send :define_method, :inspect, lambda{"foo=#{foo}; bar=#{bar};
baz=#{baz}"}
==>#<Proc:0x0006149c@(irb):8>
#inspect it:
c.new
==>foo=23; bar=42; baz=93
#change a value
baz = 144
==>144
c.new
==>foo=23; bar=42; baz=144


In Ruby 2.0, you will be able to do something like this:

c = Class.new
foop = lambda {|&b| b.call * 5 }
c.senddefine_method, :foo, foop)

But, currently, I think there is no way to do that. I suppose you could
do this:

c=Class.new
==>#<Class:0x8c5ac>
def foop() yield*2 end
==>nil
c.senddefine_method, :foo, methodfoop))
==>#<Method: Object#foop>
c.new.foo{5}
==>10

... But I get the feeling you are looking for a way to define methods
using only methods.

cheers,
Mark

 

[nobu.nokada]

Hi,

At Thu, 10 Jun 2004 05:24:21 +0900,
Mark Hubbart wrote in [ruby-talk:102995]:

In Ruby 2.0, you will be able to do something like this:

c = Class.new
foop = lambda {|&b| b.call * 5 }
c.senddefine_method, :foo, foop)

It has been implemented in 1.9.

Tue May 25 11:54:13 2004 Nobuyoshi Nakada <[email protected]>

* eval.c (rb_yield_0, proc_invoke, proc_arity): allow passing a block
to a Proc. [ruby-dev:23533]

* parse.y (block_par, block_var): ditto.

 

[Mark Hubbart]

Hi,

At Thu, 10 Jun 2004 05:24:21 +0900,
Mark Hubbart wrote in [ruby-talk:102995]:

In Ruby 2.0, you will be able to do something like this:

c = Class.new
foop = lambda {|&b| b.call * 5 }
c.senddefine_method, :foo, foop)

It has been implemented in 1.9.

Tue May 25 11:54:13 2004 Nobuyoshi Nakada <[email protected]>

* eval.c (rb_yield_0, proc_invoke, proc_arity): allow passing a block
to a Proc. [ruby-dev:23533]

* parse.y (block_par, block_var): ditto.

Well, then, that's a great reason for me to upgrade...

On a related note, it's a little difficult for me to find out when
these different things are implemented... What's the best way for a
person to see all the features that have been implemented since their
last update of the 1.9 build?

cheers,
Mark

 

[nobu.nokada]

Hi,

At Thu, 10 Jun 2004 14:16:14 +0900,
Mark Hubbart wrote in [ruby-talk:103045]:

On a related note, it's a little difficult for me to find out when
these different things are implemented... What's the best way for a
person to see all the features that have been implemented since their
last update of the 1.9 build?

We provide a wiki for commentary about changes in Japanese. At
least you could read original commit log and so on.

http://rrr.jin.gr.jp/rwiki?cmd=view;name=ruby-cvs

 

[Csaba Henk]

Mark Hubbart wrote in [ruby-talk:102995]:

In Ruby 2.0, you will be able to do something like this:

c = Class.new
foop = lambda {|&b| b.call * 5 }
c.senddefine_method, :foo, foop)

It has been implemented in 1.9.

Tue May 25 11:54:13 2004 Nobuyoshi Nakada <[email protected]>

* eval.c (rb_yield_0, proc_invoke, proc_arity): allow passing a block
to a Proc. [ruby-dev:23533]

* parse.y (block_par, block_var): ditto.

That's cool, thanks!

--
Csaba

"There's more to life, than books, you know but not much more..."
[The Smiths]
***
If you want to send me a mail, see it in the mailto link at
http://www.renyi.hu/~ekho/egyelore.html