Yield Example in Ruby For Rails book

rubyonrails-talk
1

I am going through the Ruby for Rails book. How do I run the following code:

class C

  def temp_chart(temps)     for temp in temps       converted = yield(temp)       puts "#{temp}\t#{converted}"     end   end      celsiuses = [0,10,20,40]   temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32}    end

c = C.new c.temp_chart(celsiuses)

I am getting error message:

NoMethodError: undefined method ‘temp_chart’ for C:Class

at top level in c.rb at line 11

TIA

2

You probably want

class C

def temp_chart(temps)

for temp in temps

converted = yield(temp)

puts “#{temp}\t#{converted}”

end

end

end

celsiuses = [0,10,20,40]

c = C.new

c.temp_chart(celsiuses)

I probably can’t explain why very well, but eventually Ruby for Rails will.

Good luck!

3

Hi --

I am going through the Ruby for Rails book. How do I run the following code:

class C

def temp_chart(temps)    for temp in temps      converted = yield(temp)      puts "#{temp}\t#{converted}"    end end

celsiuses = [0,10,20,40] temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32}

end

c = C.new c.temp_chart(celsiuses)

I am getting error message:

NoMethodError: undefined method �temp_chart� for C:Class

at top level in c.rb at line 11

Your combining two ways of doing it that don't mix; you want either this:

   class C      def something      end    end

   c = C.new    c.something

or this:

   def something    end

   something

What you're trying to do is like this:

   class C      def something      end

     something # won't run in this context; it needs an                   # instance of C    end

Also, note that celsiuses is a local variable, so the celsiuses inside the class definition block won't be the same as the celsiuses outside it.

David

4

I ran the code as given in the book:

def temp_chart(temps)   for temp in temps     converted = yield(temp)     puts "#{temp}\t#{converted}"   end end celsiuses = [0,10,20,30,40,50,60,70,80,90,100] temp_chart(celsiuses) {|cel| cel * 9 / 5 + 32 }

This runs fine. I was under the impression it must be part of a class. I am still confused how I could use yield from within a class. Where should the yield block be defined?

5

When I run that code I get:

LocalJumpError: no block given

method temp_chart in c.rb at line 5 method temp_chart in c.rb at line 4

6

That gave me an idea, ha, this looks like some kind_of? class
initialization... :smiley:

class X      def self.ordinary_class_method_is_to(&block)          block.call      end      def ordinary_instance_method_is_to(&block)          block.call      end

     ordinary_class_method_is_to do          puts 'Buy bags...'      end end

x = X.new x.ordinary_instance_method_is_to do      puts 'Give away...' end

7

Hi --

8

I found the fix, the problem is that it was expecting the block: {|cel| cel * 9 / 5 + 32} after the name. Now it runs fine.