Question on blocks


#1

I am new to ruby from java and had a question on blocks.

Can a block be applied to a writeable attribute or setter? I keep
getting
errors so I

am assuming no but I wanted to double check in case my syntax is
incorrect.

Thanks for the help,

Jeff

class Test

def initialize(one, two)

@one = one

@two = two

end

def one=(one)

@one = one;

Yield;

end

attr_reader :one, :two

attr_writer :two

end

test = Test.new(“Hello”, 2);

test.one = 3 { puts “Test Block” }


#2

Can anyone explain this: ?

class A
def x
yield
end

 def x=a
     yield
 end

end

a=A.new
a.x{p “called”}
a.x=1 do
p “called”
end

…/test.rb:13: parse error, unexpected kDO, expecting $

lopex


#3

Patrick,

Thanks for the quick response. I agree that it doesn’t make sense
unless I was passing the new value back to the block. I am about
15 minutes into the Picaxe and was just trying to get a handle on the
syntax. The language looks great. My brain is just hardwired with java
syntax at this point :slight_smile:

Cheers,
Jeff


#4

On 3/31/06, Jeff T. removed_email_address@domain.invalid wrote:

attr_reader :one, :two

test = Test.new(“Hello”, 2);

test.one = 3 { puts “Test Block” }

You are correct it is not allowed, but I am curious why you want to do
this? Also if I were to go and write a setter that took a block,
wouldn’t you either pass the new value into the block or use the
result of the block to set the variable?

class Test
def a=(a)
@a = a
yield @a if block_given?
end

#or
def b=(b)
@b = (block_given?) ? yield b : b
end
end

pth


#5

On 3/31/06, Patrick H. removed_email_address@domain.invalid wrote:

end

#or
def b=(b)
@b = (block_given?) ? yield b : b
end
end

pth

Sorry just to be clear, I do not think that method= methods are
allowed to take anything more than a single parameter – when using
the normal “call” syntax.

Of course you can send a message to it with a block:

class A
attr_reader :a
def a=(a,&b)
@a = block_given? ? yield(a) : a
end
end

a=A.new
a.a = 7
p a.a
a.a = 1
bl = Proc.new { |v| v * 6 }
a.send “a=”, 7, &bl
p a.a