Question about blocks

ruby-talk
1

Hello,

How can I return a value from a block? “return” immediately returns from
the caller method, “break” bypasses the called method (which yielded the
block).

I have read something about this, but cannot remember where. I know the
syntax changed between 1.6.8 and 1.8.

Ferenc

2

How can I return a value from a block? “return” immediately returns from
the caller method, “break” bypasses the called method (which yielded the
block).

I have read something about this, but cannot remember where. I know the
syntax changed between 1.6.8 and 1.8.

How about this code?

ruby a.rb
before
after result=42
expand -t2 a.rb
def test(&block)
puts “before”
res = nil
begin
res = block.call
rescue LocalJumpError => e
res = e.exit_value
end
puts “after result=#{res}”
end

test { return 42 }

···

On Wed, 21 Jan 2004 05:37:48 +0900, Ferenc Engard wrote:

–
Simon Strandgaard

3

Hi,

···

At Wed, 21 Jan 2004 05:37:48 +0900, Ferenc Engard wrote:

How can I return a value from a block? “return” immediately returns from
the caller method, “break” bypasses the called method (which yielded the
block).

next value

–
Nobu Nakada

4

Simon Strandgaard wrote:

How can I return a value from a block? “return” immediately returns from
the caller method, “break” bypasses the called method (which yielded the
block).

I have read something about this, but cannot remember where. I know the
syntax changed between 1.6.8 and 1.8.

How about this code?

ruby a.rb
before
after result=42
expand -t2 a.rb
def test(&block)
puts “before”
res = nil
begin
res = block.call
rescue LocalJumpError => e
res = e.exit_value
end
puts “after result=#{res}”
end

test { return 42 }

–
Simon Strandgaard

By way of explanation, I believe the difference is this: when the block
is invoked implicitly (via ‘yield’) a ‘return’ or ‘break’ will affect a
scope greater than itself (not sure if my terminology is correct here).
When the block is invoked explicitly (via the ‘call’ method of Proc),
then ‘return’ and ‘break’ affect only the block itself.

Perhaps some Ruby guru could verify whether this is accurate or not.
This seems to be the behavior as I’ve seen it, at least according to my
few forays into the Ruby source code.

···

On Wed, 21 Jan 2004 05:37:48 +0900, Ferenc Engard wrote:

–
Jamis Buck
jgb3@email.byu.edu

ruby -h | ruby -e ‘a=;readlines.join.scan(/-(.)[e|Kk(\S*)|le.l(…)e|#!(\S*)/) {|r| a << r.compact.first };puts “\n>#{a.join(%q/ /)}<\n\n”’

5

How can I return a value from a block? “return” immediately returns from
the caller method, “break” bypasses the called method (which yielded the
block).

I have read something about this, but cannot remember where. I know the
syntax changed between 1.6.8 and 1.8.

How about this code?

I am using cygwin on XP and I get the following :
$ ./a.rb
before

ruby a.rb
before
after result=42
expand -t2 a.rb
def test(&block)
puts “before”
res = nil
begin
res = block.call
rescue LocalJumpError => e
res = e.exit_value
end
puts “after result=#{res}”
end

test { return 42 }

–
Simon Strandgaard

here is the contents of my a.rb:
#!/usr/bin/ruby

def test(&block)
puts “before”
res = nil
begin
res = block.call
rescue LocalJumpError => e
res = e.exit_value
end
puts “after result=#{res}”
end

test { return 42 }

···

On Wed, 21 Jan 2004, Simon Strandgaard wrote:

On Wed, 21 Jan 2004 05:37:48 +0900, Ferenc Engard wrote:

–
Charlie

6

How can I return a value from a block? “return” immediately returns from
the caller method, “break” bypasses the called method (which yielded the
block).

next value

Thanks, this is it. The documentation should be updated! :slight_smile:

Ferenc

7

How about this code?

I am using cygwin on XP and I get the following :
$ ./a.rb
before

Wierd… is this a bug? am I doing something wrong?

ruby -v
ruby 1.8.1 (2003-12-22) [i386-freebsd5.1]

···

On Wed, 21 Jan 2004 08:03:33 +0900, Charles Mills wrote:

On Wed, 21 Jan 2004, Simon Strandgaard wrote:

–
Simon Strandgaard

8

Here is my version info:
$ ruby -v
ruby 1.8.0 (2003-08-04) [i386-cygwin]

I am not sure how ruby is suppost to behave in this instance.

···

On Wed, 21 Jan 2004, Simon Strandgaard wrote:

On Wed, 21 Jan 2004 08:03:33 +0900, Charles Mills wrote:

On Wed, 21 Jan 2004, Simon Strandgaard wrote:

How about this code?

I am using cygwin on XP and I get the following :
$ ./a.rb
before

Wierd… is this a bug? am I doing something wrong?

ruby -v
ruby 1.8.1 (2003-12-22) [i386-freebsd5.1]

–
Simon Strandgaard

–
Charlie