I certainly appreciate your attempts to make me get it. I think I am close. The only weird thing is I was not sure whether
"surprising" if (1+1 != 2)
is an "expression" and if yes, what its value was. I thought that this expression is same as ("surprising" if (1+1 != 2)) and both should evaluate to the same value.
They _are_ the same and they do evaluate to the same value. However, the point which probably hasn't become clear so far is this: the assignment is part of the expression that's conditionally evaluated. If the expression isn't evaluated, no assignment happens.
x = 0
(x = 1) if false
x = 1 if false # same as above
In this case the assignment with 1 is never executed and hence the value of the variable does not change. The result of the _whole_ expression however is either nil (in case of the condition evaluating to false) or the result of evaluating the expression before the "if".
Assignments happen to be defined as expressions in Ruby (everything is - there is no distinction between statement and expression like in some other languages). So they have a result like evaluating any other expression like (1 + 3) for example. The way it is defined the result of an assignment expression is the right hand side. You can view the change of the variable as a side effect of evaluating the assignment expression.
That's also the reason why you can do assignment chains like
a = b = c = 0
Assignments are evaluated right to left (as opposed to 1 + 2 + 3 for example which is evaluated left to right). The result of "c = 0" is a) c now points to object 0 and b) 0 is also returned as result of evaluating this, so in the end you get
(a = (b = (c = 0)))
Thus, whereas now I get that the value of ("surprising" if (1+1 != 2)) is nil, it is not clear to me if
- "surprising" if (1+1 != 2) is an expression and evaluates to some/same value.
Yes, it is an expression and evaluates the way I have tried to outline above. Everything is an expression in Ruby, even a case statement which comes in handy from time to time:
foo = case x
when String
"it's a String"
when Fixnum, Integer, Float
"it's a number"
else
"I have no idea"
end
puts foo
A final remark, if your aim is to assign nil in case the condition is false, the ternary operator is probably a better choice:
s = (1+1 != 2) ? "surprising" : nil
s = 1+1 != 2 ? "surprising" : nil
s = 1+1 == 2 ? nil : "surprising"
You can as well use if else which is more verbose
s = if (1+1 != 2) then "surprising" else nil end
The main point is to make the assignment unconditional.
Apologies if this is becoming rather lengthy.
No worries. That's ok.
Kind regards
robert
···
On 10.01.2009 04:43, Kedar Mhaswade wrote:
--
remember.guy do |as, often| as.you_can - without end
