es sólo para el azúcar sintáctica.
For ... In
Earlier we said that the only built-in Ruby looping primitives were while and until. What's this ``for'' thing, then? Well, for is almost a lump of syntactic sugar. When you write
for aSong in songList
aSong.play
end
Ruby translates it into something like:
songList.each do |aSong|
aSong.play
end
The only difference between the for loop and the each form is the scope of local variables that are defined in the body. This is discussed on page 87.
You can use for to iterate over any object that responds to the method each, such as an Array or a Range.
for i in ['fee', 'fi', 'fo', 'fum']
print i, " "
end
for i in 1..3
print i, " "
end
for i in File.open("ordinal").find_all { |l| l =~ /d$/}
print i.chomp, " "
end
produces:
fee fi fo fum 1 2 3 second third
As long as your class defines a sensible each method, you can use a for loop to traverse it.
class Periods
def each
yield "Classical"
yield "Jazz"
yield "Rock"
end
end
periods = Periods.new
for genre in periods
print genre, " "
end
produces:
Classical Jazz Rock
Ruby no tiene otras palabras clave de comprensión (como el ejemplo que acaba de realizar la suma). for
no es una palabra clave terriblemente popular, y la sintaxis del método (arr.each {}
) es generalmente preferida.
Guau, tan sutil, pero será útil cuando me encuentre con algo como esto. ¡Gracias! – sivabudh
En realidad, su segundo ejemplo arroja 'NameError: variable local indefinida o método 'i' para main: Object'. Es porque te falta un 'hacer'. –
@JakubHampl Lo arreglé. ¡Gracias! –