Newbie question

is in ruby operator for:

a = b if b

a (operator) b

?

On 10/03/2008, Frantisek P. [email protected] wrote:

is in ruby operator for:

a = b if b

a (operator) b

a ||= b

Farrel

Farrel L. wrote:

On 10/03/2008, Frantisek P. [email protected] wrote:

a = b if b

a ||= b

Nope.
a ||= b is equivalent to a = a || b is equivalent to
a = if a then a else b end is NOT equivalent to a = b if b

HTH,
Sebastian

On Mon, Mar 10, 2008 at 11:50 AM, Farrel L.
[email protected] wrote:

a ||= b

That’s not right. It will give you a NameError, that b is undefined.
a ||= b
is equivalent to
a = a || b
which is the same as
a = b if not a

a = b if b

I know of no operator for it yet.

On Mon, Mar 10, 2008 at 11:50 AM, Farrel L.
[email protected] wrote:

On 10/03/2008, Frantisek P. [email protected] wrote:

is in ruby operator for:

a = b if b

a (operator) b

a ||= b

Farrel

a ||= b is

a = a || b
that is
a = b if !a
that is
a = b unless a

It is equal to “a = b if b” if both a and b are of boolean type
(doesn’t work for e.g. numbers).

On Mon, 2008-03-10 at 19:50 +0900, Farrel L. wrote:

On 10/03/2008, Frantisek P. [email protected] wrote:

is in ruby operator for:

a = b if b

a (operator) b

a ||= b

Not quite:

irb(main):007:0> a = 1
=> 1
irb(main):008:0> b = 2
=> 2
irb(main):009:0> a ||= b
=> 1
irb(main):010:0>
irb(main):011:0* a
=> 1
irb(main):012:0> a = b if b
=> 2
irb(main):013:0> a
=> 2

a ||= b is equivalent to a = b if !a, which isn’t quite the same thing
as a = b if b.

On Mar 10, 11:50 am, Farrel L. [email protected] wrote:

On 10/03/2008, Frantisek P. [email protected] wrote:

is in ruby operator for:

a = b if b

a (operator) b

a ||= b

“a ||= b” means “a = b unless a”.

I don’t think there is an operator for “a = b if b”.

Luckily, “a = b if b” is valid ruby code. “a = b || a” or “a = (b or
a)” would also work.

yes, i can write

a = b || a

but isn’t it more complex. imagine that b is nil. then a = a will be
evaluated?

maybe time for feature request? new operator a =|| (a = b if b)

(variable = params[:nice_symbol] if params[:nice_symbol] doesnt look
very nice)

Lars wrote:

On Mar 10, 11:50 am, Farrel L. [email protected] wrote:

On 10/03/2008, Frantisek P. [email protected] wrote:

is in ruby operator for:

a = b if b

a (operator) b

a ||= b

“a ||= b” means “a = b unless a”.

I don’t think there is an operator for “a = b if b”.

Luckily, “a = b if b” is valid ruby code. “a = b || a” or “a = (b or
a)” would also work.

On Mon, Mar 10, 2008 at 7:11 AM, Frantisek P.
[email protected] wrote:

yes, i can write

a = b || a

but isn’t it more complex. imagine that b is nil. then a = a will be
evaluated?

Then why not just “a = b if b”?

maybe time for feature request? new operator a =|| (a = b if b)

(variable = params[:nice_symbol] if params[:nice_symbol] doesnt look
very nice)

Doesn’t bother me, its a lot more clear than variable =||
params[:nice_symbol].
More operators that look similar and have similar but subtly different
meanings
is less immediate visual clarity.

On Mar 10, 9:04 am, Rados³aw Bu³at [email protected] wrote:

Direction for Ruby future should be to clean those ugly perlism from
Ruby (for example magic variable $_)

$_ is no more magic than ARGV.

Paul Graham’s new language Arc uses _ for a similar purpose.

On Mon, Mar 10, 2008 at 3:11 PM, Frantisek P.
[email protected] wrote:

very nice)
And after x years later we would have another Perl. I don’t like to
have gazillions operators for all occasions.
a = b if b is that hard to write and read? I don’t think so :).
Direction for Ruby future should be to clean those ugly perlism from
Ruby (for example magic variable $_), rather that to add new stuff
like that.


Rados³aw Bu³at

http://radarek.jogger.pl - mój blog

On Tue, Mar 11, 2008 at 6:18 AM, Benjamin Oakes
[email protected] wrote:

puts(“out: #{out.inspect}”)

out: nil

Because your first test will be different if “out” already exists and
is not nil. The OP wants “out” to change only if “some_variable” is
not nil.

Todd

On Mon, Mar 10, 2008 at 9:11 AM, Frantisek P.
[email protected] wrote:

very nice)

a = b if b
a)" would also work.


Posted via http://www.ruby-forum.com/.

I guess I don’t understand what the point of having a = b if b is.
The only thing I can see that’s different than a ||= b is that false
will become nil. Here’s what I tried:

def demo(some_value)
out = some_value if some_value
puts(“out: #{out.inspect}”)
out = nil || some_value
puts(“out: #{out.inspect}”)
out = some_value
puts(“out: #{out.inspect}”)
a_different_variable ||= some_value
puts(“a_different_variable: #{a_different_variable.inspect}”)
puts(’------------’)
end

demo(nil)
demo(88)
demo(false)

Outputs:

out: nil
out: nil
out: nil
a_different_variable: nil

out: 88
out: 88
out: 88
a_different_variable: 88

out: nil
out: false
out: false
a_different_variable: false

So… Why doesn’t ||= work for how you’re using it? (Why do you want
the “b if b” behavior?)

– Ben (aka divokz)

2008/3/11 William J. [email protected]:

On Mar 10, 9:04 am, Rados³aw Bu³at [email protected] wrote:

Direction for Ruby future should be to clean those ugly perlism from
Ruby (for example magic variable $_)

$_ is no more magic than ARGV.

I don’t get it. ARGV is for program parameters. All languages have it
but of course maybe in different way (like java String[] args in main
method). Where is magic here?


Rados³aw Bu³at

http://radarek.jogger.pl - mój blog