Blocks and scoping question

[Mischa Fierer]

Hello,

The following makes sense to me:

lambda {|x| puts x; [1,2].collect{|x| x+1} }.call("aaa")
aaa
=> [2, 3]

The following does not so much:

lambda {|x| puts x; [1,2].collect{|x| x+1}; puts x }.call("aaa")
aaa
2
=> nil

Why is the final puts x not return a?

 

[Stefano Crocco]

Hello,

The following makes sense to me:

lambda {|x| puts x; [1,2].collect{|x| x+1} }.call("aaa")
aaa
=> [2, 3]

The following does not so much:

lambda {|x| puts x; [1,2].collect{|x| x+1}; puts x }.call("aaa")
aaa
2
=> nil

Why is the final puts x not return a?

Because puts always returns nil:

ri IO#puts

---------------------------------------------------------------- IO#puts
ios.puts(obj, ...) => nil

 

[Mischa Fierer]

A friend informs me that this is changed in 1.9

For this who are interested:

http://groups.google.com/group/sbonrails/browse_thread/thread/cfcfdad71d8f786c

Hello,

The following makes sense to me:

lambda {|x| puts x; [1,2].collect{|x| x+1} }.call("aaa")
aaa
=> [2, 3]

The following does not so much:

lambda {|x| puts x; [1,2].collect{|x| x+1}; puts x }.call("aaa")
aaa
2
=> nil

Why is the final puts x not return a?

 

[Mischa Fierer]

lambda {|x| puts x; [1,2].collect{|x| x+1}; puts x }.call("aaa")
aaa
2
=> nil

Why is the final puts x not return a?

Because puts always returns nil:

ri IO#puts

---------------------------------------------------------------- IO#puts
ios.puts(obj, ...) => nil

Sorry, phrased this wrong, i wasn't looking at the return value, but the
2 above it.

 

[Peña, Botp]

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IHgNCmFhYQ0KYWFhDQoNCg==

 

[Thomas B.]

Hello,

The following makes sense to me:

lambda {|x| puts x; [1,2].collect{|x| x+1} }.call("aaa")
aaa
=> [2, 3]

The following does not so much:

lambda {|x| puts x; [1,2].collect{|x| x+1}; puts x }.call("aaa")
aaa
2
=> nil

Why is the final puts x not return a?

It's because the x in collect{|x| ...} in fact uses the variable x that
previously contained your "aaa", because it is already defined in this
scope. If x wasn't defined at the point of calling collect, then x
inside collect's block would be a separate variable each iteration.

This is going to change in Ruby 1.9, and block variables will always be
separate from variables visible in the scope.

TPR.