OpenEuphoria

Re: Parameters by Reference

• Posted by Ralf Nieuwenhuijsen <nieuwen at XS4ALL.NL> Apr 30, 1999
• 486 views

The best way, IMHO, when you want several parts of your program to share data,
independent of the 'namespace', you could use
special functions:

These examples are key-association libraries, but you could write any sort of
'data'-management-library.
The first version uses 'host'-storage, the second uses 'client'-store, I will
discuss the advantages and disadvantages,
afterwards, of the two approaches.

You use the key-association libs, as following:

    -- To store a new value
    store_key ("mykey", "myval")

    -- To set an already existing key to another value
    store_key ("mykey", "myotherval")

    -- To retrieve a value
    puts (1,     retrieve_key ("mykey")    )

    -- To 'delete' a key
    store_key ("mykey", -1)

-- Notice the special value -1.
-- This value will be returned by retrieve_key when no key matches, and setting
a key to this value will 'delete' the key.
-- This is not a problem since the value returned by retrieve_key _will_ return
the correct value.

-- keys_ex_a.e

    global constant
        TRUE = 1,
        FALSE = 0,
        NONE = -1

    sequence
        keys,
        data

    global procedure store_key (object key, object val)
     integer place

        place = find (key, keys)
        if place then
             if equal (val, -1) then
                data = data[1..place-1] & data[place+1..length(data)]
                keys = keys[1..place-1] & keys[place+1..length(keys)]
            else
                data[place] = val
            end if
        elsif equal (val, -1)
            data = append(data, val)
            keys = append(keys, key)
        end if
    end procedure

    global function retrieve_key (object key)
    integer place

        place = find (key, keys)
        if place then
            return data[place]
        else
            return -1
        end if
    end function

--- This second example works like this:

    -- Creating a new data-base
        keydb my_kl
        my_kl = new_keydb

    -- Storing a new key
    my_kl = store_key (my_kl, "mykey", "myval")

    -- Setting that key to a new value
    my_kl = store_key (my_kl, "mykey", "myotherval")

    -- 'Deleting' that key
    my_kl = store_key (my_kl, "mykey", NONE)     -- none equals -1

    -- Retrieving a key
    puts (1,     retrieve_key (my_kl, "mykey")     )

----- keys_ex_b.e    -- Client-side data storage

    global constant
        TRUE = 1,
        FALSE = 0,
        NONE = -1

    type keydb (object x)
if sequence (x) and length(x) = 2 and sequence (x[1]) and sequence
        (x[2]) then
            return length(x[1]) = length(x[2])
        else
            return 0
        end if
    end type

    global function new_keydb ()
        return {{},{}}
    end function

    global function store_key (keydb kl, object key, object val)
    sequence keys, data
     integer place

        keys = kl[1]
        data = kl[2]

        place = find (key, keys)
        if place then
             if equal (val, -1) then
                data = data[1..place-1] & data[place+1..length(data)]
                keys = keys[1..place-1] & keys[place+1..length(keys)]
            else
                data[place] = val
            end if
        elsif equal (val, -1)
            data = append(data, val)
            keys = append(keys, key)
        end if

        return {keys, data}
    end function

    global function retrieve_key (keydb kl, object key)
    sequence data, keys
    integer place

        keys = kl[1]
        data = kl[2]

        place = find (key, keys)
        if place then
            return data[place]
        else
            return -1
        end if
    end function

--------------------------------------------------------------------------------------------------------------------------------
------------
Advantages of the server-side storage (ps. these terms are made up by me, there
are not official technical terms, or anything):

    + There are no namespace problems.
    + It easier to use

Advantages of the client-side storage:

    + You can have multiple databases
+ You can store a database, print it out, or store it inside any type of
    structure, and therefor you could say, you get a
lot more control over the data. You can copy two databases, etc.
+ Different libraries support the same datatype can work with the data in
    the same way the library does. (that is, change
the variable and return it), you wouldn't notice in difference in handling.

And off course all of 'advantages' could be achieved by expending the first
example, with many more routines to clear the
database, create and setup multiple databases, to store a database, etc. However
the initiative can only come from the original
library, any user can not later on, add routines to his program that do this,
since he can not access the variable at all.

Ralf N.
nieuwen at xs4all.nl
ralf_n at email.com