Ruby Language Blocks and Procs and Lambdas
Syntax
- Proc.new(block)
- lambda { |args| code }
- ->(arg1, arg2) { code }
- object.to_proc
- { |single_arg| code }
- do |arg, (key, value)| code end
Remarks
Be careful about operator precedence when you have a line with multiple methods chained, like:
str = "abcdefg"
puts str.gsub(/./) do |match|
rand(2).zero? ? match.upcase : match.downcase
end
Instead of printing something like abCDeFg, like you'd expect, it prints something like #<Enumerator:0x00000000af42b28> -- this is because do ... end has lower precedence than methods, which means that gsub only sees the /./ argument, and not the block argument. It returns an enumerator. The block ends up passed to puts, which ignores it and just displays the result of gsub(/./).
To fix this, either wrap the gsub call in parentheses or use { ... } instead.
