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Ruby Programming CS 132A

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Somedude says By now you know that Ruby uses blocks for iteration. This is a core feature of Ruby. You remember that a block is some code between curly braces.

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Ruby Programming CS 132A Somedude says By now you know that Ruby uses blocks for iteration. This is a core feature of Ruby. You remember that a block is some code between curly braces. And that blocks can only be used as arguments to methods, like this. [1,2,3].each { |i| puts i } # 1 # 2 # 3 This is the bl ock You can use a "do" block when the block is more than one line. 99.times do |n|  if n % 2 == 0    puts n.to_s + " is even."  else    puts n.to_s + " is odd."  end end # 1 is odd. # 2 is even. . # 99 is odd. Blocks and Procs R uby provid es tw o synta x es for creating blocks. (1) The Do Block The {} block is commonly used when only a single line of code is required. 99.times { |t| puts "So far, #{t} times." } # So far, 1 times. # So far, 2 times. . # So far, 99 times. Blocks and Procs And the {} Block (2) The {} Block The bracket syntax has a higher precedence than the do.end syntax. Look at these examples. 1.upto 3 do |x|  puts x end # 1 # 2 # 3 1.upto 3 {|x| puts x } # SyntaxError: compile error Blocks and Procs W arning!!! W orks fine E rror!! What w ent wrong? Blocks and Procs 1.upto 3 {|x| puts x } # SyntaxError: compile error The curly brackets have a HIGHER PRECEDENCE than the do.end block, so the block attaches to the number 3 rather than to the upto() method! Somedude says What this means is that Ruby looked at the code and saw the method and the curly brackets with the 3 between them. The curly brackets had the higher precedence, so Ruby attached the block to the "3" instead of the "upto()". {} attaches HERE! The Solution . Use parentheses! Parentheses have the highest precedence. When theres any chance that your code may be confusing to Ruby (and yourself), use parentheses. 1.upto(3) {|x| puts x } # 1 # 2 # 3 Blocks and Procs ...

Source: norbert.ccsf.cc.ca.us

 

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