From: "Mariusz Pękala" <skoot@...>
Date: 2007-07-20T21:46:24+09:00
Subject: Re: block_given? problem

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On 2007-07-20 20:19:58 +0900 (Fri, Jul), westlin9@gmail.com wrote:
> I can't figure out why the do...end block isn't detected by the
> "block_given?" function. The problem occurs when a method call with a
> block is used in a puts statement. See the code example below.
> Can some one explain this to me please? Is this a bug?
>=20
>=20
> class TheClass
>   def self.TheMethod()
>     if block_given?
>       puts "yes, block given"
>     else
>       puts "no block is given"
>     end
>     'return val'
>   end
> end
>=20
> # ok
> puts TheClass.TheMethod {|param| 123}
>=20
> # block not detected
> puts TheClass.TheMethod do |param|
>   123
> end

This is because do..end block gets attached to the 'puts' instead of
TheMethod.

do..end and {||..} differ in precedence. {||..} binds to the rightmost
method, while do..end to the leftmost one.

> # ok
> a =3D TheClass.TheMethod {|param| 123}
> puts a
>=20
> # ok
> a =3D TheClass.TheMethod do |param|
>   123
> end
> puts a

There you have no ambiguity as there is only one method call.


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