Re: Colon Operator: Superfluous Syntax?

[Brian Hagerty <Brian.Hagerty@...>]

gary ng wrote:
> --- Brian Hagerty <Brian.Hagerty@LilypadNetworks.com>
> wrote:
> > But since 'self' is a special local symbol in Lua,
> Is that true ? I think it can be called foo or bar or
> anything.

No, the self parameter in a colon-defined function can't be 
called foo or bar or anything else (as far as I understand). 
Here is the colon syntax for a OO-method definition (Blue Book 
pg 150):

function Account:deposit (v)
  self.balance = self.balance + v
end

In this case, balance is an instance variable previously defined 
in the Account table.  self is the "hidden" parameter that 
refers to the calling object (Account, in this case).

Notice that the "hidden" parameter idiom of colon-functions does 
not provide another place for you to create a different name for 
that hidden parameter.  In fact, 'self' was not explicitly 
defined anywhere in the function.  You just use it per the 
implied Lua semantics.  The semantics of the colon operator 
requires that the hidden parameter must be a local variable 
called self. -- In particular, this:

function Account:deposit (v)
  foo.balance = foo.balance + v
end

is not a way of using foo as the name of the hidden parameter. 
foo, in this case, is a reference to an outer variable, outside 
the lexical scope of the current function.

// Brian Hagerty