Re: equals metamethod and hash functions

[PA <petite.abeille@...>]

On Jun 08, 2005, at 00:27, Paul Chiusano wrote:

> I need equal objects (according to __eq) to hash to
> the same location in the table. The easiest thing would be if there
> were a __hash metamethod, but there isn't one. (or is there? it isn't
> mentioned in the documentation...)

FWIW, LU [1] happily uses string representation of complex objects and 
let Lua handle the hashing itself.

Assuming a Map [2] like structure to store "complex" objects [3]:

        -- instance method to convert a given key to a string
        this.stringForKey = function( aKey )
                if ( aKey ~= nil ) and ( type( aKey ) ~= "string" ) then
                        if ( this.isKindOf( aKey ) == true ) then
                                aKey = aKey.toString()
                        else
                                aKey = tostring( aKey )
                        end
                end

                return aKey
        end

        -- instance method to return a value for a given key
        this.get = function( aKey )
                if ( aKey ~= nil ) then
                        aKey = this.stringForKey( aKey )

                        return this.content()[ aKey ]
                end

                return nil
        end

        -- instance method to associate a given value with a given key
        this.put = function( aKey, aValue )
                if ( aKey ~= nil ) then
                        aKey = this.stringForKey( aKey )

                        this.content()[ aKey ] = aValue
                end

                return this
        end

Cheers

--
PA, Onnay Equitursay
http://alt.textdrive.com/

[1] http://dev.alt.textdrive.com/browser/lu/
[2] http://dev.alt.textdrive.com/file/lu/LUMap.lua
[3] http://dev.alt.textdrive.com/file/lu/LUObject.lua