Enumerable

[Michael Saltzman]

Am new to Ruby and have the folloiwng Question.

I have a class, say Collect, and I want to mixin Enumerable. How do I
write the each method in Collect?

class Collect
include Enumerable
def initialize()
@array = Array.new(0)
@ct = 0
end
def add(item)
@array.push(item)
@ct += 1
end
def howmany
@ct
end
def each
#
# Not sure how to do this????
#
end
end

 

[Martin DeMello]

Am new to Ruby and have the folloiwng Question.

I have a class, say Collect, and I want to mixin Enumerable. How do I
write the each method in Collect?

class Collect
include Enumerable
def initialize()
@array = Array.new(0)
@ct = 0
end
def add(item)
@array.push(item)
@ct += 1
end
def howmany
@ct
end
def each
#
# Not sure how to do this????
#
end
end

Assuming you want to iterate over @array,

def each
@array.each {|i| yield i}
end

martin

 

[A. S. Bradbury]

Am new to Ruby and have the folloiwng Question.

I have a class, say Collect, and I want to mixin Enumerable. How do I
write the each method in Collect?

class Collect
include Enumerable
def initialize()
@array = Array.new(0)
@ct = 0
end
def add(item)
@array.push(item)
@ct += 1
end
def howmany
@ct
end
def each
#
# Not sure how to do this????
#
end
end

It depends what you want each to do? Just to wrap @array.each? In that case,
this would work:
def each
@array.each {|item| yield item}
end

Of course you can do whatever you want to the array item in the block before
you yield it again.

An alternative technique is as follows:
def each(&block)
@array.each(&block)
end

I'm sure someone will correct me if I describe this slightly wonky, but the
basic idea is that the interpreter converts the block argument to a proc with
a name (I think I read an article that claimed a block is always converted to
a proc, but when no &arg is given, it is simply a proc with no name,
accessible of course via yield). This is then passed on to @array.each as a
block argument.

I don't know whether there are any real advantages or disadvantages to either
method. Hope this helps

Alex

 

[Robert Klemme]

Am new to Ruby and have the folloiwng Question.

I have a class, say Collect, and I want to mixin Enumerable. How do I
write the each method in Collect?

class Collect
include Enumerable
def initialize()
@array = Array.new(0)
@ct = 0
end
def add(item)
@array.push(item)
@ct += 1
end
def howmany
@ct
end
def each
#
# Not sure how to do this????
#
end
end

You have several options:

class Collect
include Enumerable

def initialize()
@array = []
end

def add(item)
@array.push(item)
self
end

alias :<< :add

def howmany
@array.size
end

# option 1: use yield
def each_1
@array.each {|x| yield x}
self
end

# option 2: delegate to Array's each
def each_2(&b)
@array.each(&b)
self
end
end

Kind regards

robert

 

[A. S. Bradbury]

It depends what you want each to do? Just to wrap @array.each? In that
case, this would work:
def each
@array.each {|item| yield item}
end

Of course you can do whatever you want to the array item in the block
before you yield it again.

An alternative technique is as follows:
def each(&block)
@array.each(&block)
end

I don't know whether there are any real advantages or disadvantages to
either method. Hope this helps

Just did a quick benchmark out of curiosity:
user system total real
Two yields 15.720000 2.220000 17.940000 ( 20.336562)
Pass the named block 4.130000 1.020000 5.150000 ( 5.562950)
Direct on attr_accessor 3.810000 1.010000 4.820000 ( 5.440259)

I passed the block {|i| i} and initialized @array to (1..100).to_a, and ran
through 50000 times.

Alex