ruby question about blocks

[finer recliner]

the following code:



letters = ['a','b','c','d']


letters.each do |x|

x.upcase!

if x == 'B' then
x = 'z'
end

end

puts letters

produces this output:


$ ruby test.rb
A
B
C
D



how come inside the "each" block, the upcase! method worked, but the assignment operator inside the "if" statement did not work?

if it was as simple as "x" is a local variable in the "each" block, then wouldn't both the upcase! method and the assignment operator not stick when you exit the loop?

how can i make the the assignment operator stick even after exiting the loop?

thanks guys.

[CptPicard]

This is one of these pass-by-value vs. pass by reference and "what is exactly being set by =" questions :)

The reason why the uppercase thing works is that x.uppercase! takes the object referred to by the variable x and mutates it to being uppercase. When you do x = 'z', what it actually does is that it rebinds the name x to a new value 'z'. What you're doing with '=' is just simply making the parameter name x "mean something else" inside the block.

Some ruby guru (mssever) can answer the how to make it stick question :)

[stylishpants]

Essentially what you're trying to do is use a closure to create a little function that modifies each element in your array. You can use the 'map!' function to modify your array in place.



letters = ['a','b','c','d']

letters.map! { |x|
x.upcase!

if x == 'B'
'x'
else
x
end
}

puts letters


Note that each array element is being set to the final value in the closure, which is why the values within the 'if' statement need not be explicitly assigned to a variable.

Type "ri Array.map" for more information.

[finer recliner]

thanks guys, the map! method was just what i needed

:guitar: