We can iterate an Array / list in ruby in two ways:
Using the for x in y syntax:
> for x in [1,2,3] do
> puts x
> end
1
2
3
=> [1, 2, 3]
Using the method .each
> [1,2,3].each do |x|
> puts x
> end
1
2
3
=> [1, 2, 3]
What's the difference between them, and when should I use one or the other?
They are equivalent.
for a in b; code end is a syntax sugar for b.each {|a| code } , with the difference that the a variable does not have its scope limited to the block. A simple proof for this is as follows:
class A
def each(&block)
block.call(1)
block.call(2)
block.call(42)
end
end
for x in A.new
p x
end
# mostra 1, 2 e 42
p x # mostra 42
# a variável ainda está viva aqui, é a única diferença
There was a performance difference where for was less efficient than each , but that's not significant since Ruby 2.0 .
As a reference, part of compile.c :
// Ao encontrar um "for"
if (nd_type(node) == NODE_FOR) {
COMPILE(ret, "iter caller (for)", node->nd_iter);
// Crie um bloco para ele
iseq->compile_data->current_block =
NEW_CHILD_ISEQVAL(node->nd_body, make_name_for_block(iseq),
ISEQ_TYPE_BLOCK, line);
// Crie uma invocação ao método "each" passando o bloco
ADD_SEND_R(ret, line, ID2SYM(idEach), INT2FIX(0),
iseq->compile_data->current_block, INT2FIX(0));
}
Note that ruby is much more idiomatic and preferable to use each instead of for , but this is more a matter of style than practice.