Hi,
Say you have a method in a class that's defined as this:
(working from Peter Cooper's Beginning Ruby book, p. 155 of the book)
class Dungeon
.
.
.
def start(location)
@player.location = location
show_current_description
end
why is it that when you place the player in the large cave, it's
my_dungeon.start(:largecave)
instead of
my_dungeon.start(largecave)
?
why is largecave a symbol?
Thanks so much!
--
Posted via http://www.ruby-forum.com/.
A symbol and a variable are two different things. A symbol is
essentially a special kind of literal, just like a number or a string
is. You cannot assign values to symbols, just like you can't assign
values to numbers or strings -- they are their own values. That is, it
makes no sense to say `42 = "banana"`, just as it makes no sense to
say `:banana = 42`.
In this case, the author is using the symbol :largecave to represent a
particular location. The reason why he might prefer a symbol literal
to a string literal is that symbols are immutable. "Immutable" means
that you can't do operations on symbols to change them (unlike, say,
strings). Immutability is a good property because it decreases that
number of surprises you can have, and because it makes reasoning about
your program easier.
~ jf
--
John Feminella
Principal Consultant, BitsBuilder
LI: http://www.linkedin.com/in/johnxf
SO: User John Feminella - Stack Overflow
On Tue, Feb 15, 2011 at 19:41, Gaba Luschi <friedoysterlover@gmail.com> wrote:
Hi,
Say you have a method in a class that's defined as this:
(working from Peter Cooper's Beginning Ruby book, p. 155 of the book)class Dungeon
.
.
.def start(location)
@player.location = location
show_current_description
endwhy is it that when you place the player in the large cave, it's
my_dungeon.start(:largecave)instead of
my_dungeon.start(largecave)
?
why is largecave a symbol?
Thanks so much!--
Posted via http://www.ruby-forum.com/\.
Another way to look at it is a symbol is it is an emnumerated scalar.
You could have
cavesize = 345
my_dungeon.start(cavesize)
However if caves are only ever Small, Medium and Large, then you can
represent that finite set of options by passing :smallcave, :mediumcave
or :largecave.
A symbol can therefore more closely represent the logic of the problem.
--
Posted via http://www.ruby-forum.com/.
This is quite good tutorial about symbols and strings here
http://www.robertsosinski.com/2009/01/11/the-difference-between-ruby-symbols-and-strings/
On Wed, Feb 16, 2011 at 6:38 AM, John Feminella <johnf@bitsbuilder.com>wrote:
A symbol and a variable are two different things. A symbol is
essentially a special kind of literal, just like a number or a string
is. You cannot assign values to symbols, just like you can't assign
values to numbers or strings -- they are their own values. That is, it
makes no sense to say `42 = "banana"`, just as it makes no sense to
say `:banana = 42`.In this case, the author is using the symbol :largecave to represent a
particular location. The reason why he might prefer a symbol literal
to a string literal is that symbols are immutable. "Immutable" means
that you can't do operations on symbols to change them (unlike, say,
strings). Immutability is a good property because it decreases that
number of surprises you can have, and because it makes reasoning about
your program easier.~ jf
--
John Feminella
Principal Consultant, BitsBuilder
LI: http://www.linkedin.com/in/johnxf
SO: User John Feminella - Stack OverflowOn Tue, Feb 15, 2011 at 19:41, Gaba Luschi <friedoysterlover@gmail.com> > wrote:
> Hi,
> Say you have a method in a class that's defined as this:
> (working from Peter Cooper's Beginning Ruby book, p. 155 of the book)
>
> class Dungeon
> .
> .
> .
>
> def start(location)
> @player.location = location
> show_current_description
> end
>
> why is it that when you place the player in the large cave, it's
> my_dungeon.start(:largecave)
>
> instead of
> my_dungeon.start(largecave)
> ?
> why is largecave a symbol?
> Thanks so much!
>
> --
> Posted via http://www.ruby-forum.com/\.
>
>
Another way to look at it is a symbol is it is an emnumerated scalar.
I don't think that's an accurate characterization, imo, since symbols
have no relationship or knowledge of other symbols. They are not a
collection of anything, and thus by definition can't be an
enumeration. Using your example, nothing stops you from writing
my_dungeon.start(:bananas)
and that would be a perfectly valid parameter to supply. However, if
you wrote something like
my_dungeon.start(DungeonSizes[:bananas])
that would clue you into the problem. In this case, DungeonSizes would
be more like the enumeration, into which a symbol would be the index
for the element of the enumeration you wanted to select.
~ jf
--
John Feminella
Principal Consultant, BitsBuilder
LI: http://www.linkedin.com/in/johnxf
SO: User John Feminella - Stack Overflow
On Wed, Feb 16, 2011 at 10:34, Mike Stephens <rubfor@recitel.net> wrote:
Another way to look at it is a symbol is it is an emnumerated scalar.
You could have
cavesize = 345
my_dungeon.start(cavesize)However if caves are only ever Small, Medium and Large, then you can
represent that finite set of options by passing :smallcave, :mediumcave
or :largecave.A symbol can therefore more closely represent the logic of the problem.
--
Posted via http://www.ruby-forum.com/\.
Along with what John Feminella said about symbols' immutability is the
advantage they have over the string literals that they also often replace,
and that is the fact that each new instance of a string literal will refer
to a different Ruby object while each reference to the equivalent symbol
will refer to the same object instance with the added bonus that less memory
is used. See the example below.
ruby-1.9.2-p136 :001 > "hi".object_id
=> 71175750
ruby-1.9.2-p136 :002 > "hi".object_id
=> 71172980
ruby-1.9.2-p136 :003 > :hi.object_id
=> 185928
ruby-1.9.2-p136 :004 > :hi.object_id
=> 185928
On Wed, Feb 16, 2011 at 5:04 AM, sanjeev mathur <learnsanjeev@gmail.com>wrote:
This is quite good tutorial about symbols and strings here
http://www.robertsosinski.com/2009/01/11/the-difference-between-ruby-symbols-and-strings/
On Wed, Feb 16, 2011 at 6:38 AM, John Feminella <johnf@bitsbuilder.com > >wrote:
> A symbol and a variable are two different things. A symbol is
> essentially a special kind of literal, just like a number or a string
> is. You cannot assign values to symbols, just like you can't assign
> values to numbers or strings -- they are their own values. That is, it
> makes no sense to say `42 = "banana"`, just as it makes no sense to
> say `:banana = 42`.
>
> In this case, the author is using the symbol :largecave to represent a
> particular location. The reason why he might prefer a symbol literal
> to a string literal is that symbols are immutable. "Immutable" means
> that you can't do operations on symbols to change them (unlike, say,
> strings). Immutability is a good property because it decreases that
> number of surprises you can have, and because it makes reasoning about
> your program easier.
>
> ~ jf
> --
> John Feminella
> Principal Consultant, BitsBuilder
> LI: http://www.linkedin.com/in/johnxf
> SO: User John Feminella - Stack Overflow
>
>
>
> On Tue, Feb 15, 2011 at 19:41, Gaba Luschi <friedoysterlover@gmail.com> > > wrote:
> > Hi,
> > Say you have a method in a class that's defined as this:
> > (working from Peter Cooper's Beginning Ruby book, p. 155 of the book)
> >
> > class Dungeon
> > .
> > .
> > .
> >
> > def start(location)
> > @player.location = location
> > show_current_description
> > end
> >
> > why is it that when you place the player in the large cave, it's
> > my_dungeon.start(:largecave)
> >
> > instead of
> > my_dungeon.start(largecave)
> > ?
> > why is largecave a symbol?
> > Thanks so much!
> >
> > --
> > Posted via http://www.ruby-forum.com/\.
> >
> >
>
>