On Tue, 25 May 2010, Szak�ts Viktor wrote:
Hi,
> That sounds great, may I ask for a simple example which
> show the usefulness of this feature over regular hashes?
This code illustrates the difference between regular and
associative hash arrays:
proc main()
local h
h := { => }
? "regular hash array"
tst( h )
h := { => }
? "associative hash array"
hb_hKeepOrder( h, .T. )
tst( h )
return
proc tst( h )
local v, i
h[ 'zxc' ] := 1.000
h[ 'qwe' ] := 2.000
h[ 'abc' ] := 3.000
h[ 'dfg' ] := 4.000
h[ 'rbc' ] := 5.000
? "for each:"
for each v in h
? v:__enumIndex(), v:__enumKey(), v
next
? "access by index:"
for i := 1 to len( h )
? i, hb_hValueAt( h, i )
next
?
return
As you can see executing it the order of items in associative array
is strictly defined and it's the same as the order in which new item
were added. It means that you have two strictly defined indexes. One
which can be used with [] operator and any hash item keys and the
second numeric only index. It's usable in many different places.
This is the part of ChangeLog message I created for Harbour OLE
servers. It's very nice example of practical usage.
<hAction> is optional parameter with hash array containing messages
and instance variables used by OLE server. The keys in hash array
are strings with message names and values are actions. Codeblock
and symbol items means that given message is a method call and
any other value means that it's variable.
By default the same hash array is shared between all objects
created by registered server. It's important when hash array
contains values which are neither codeblock nor symbol items
so they are not used as method but rather as instance variables
because such instance variables are shared between OLE objects.
Setting 4-th parameter <lHashClone> to .T. causes that each
objects receives it's own copy of <hAction> item so instance
variables inside hash array are also local to OLE object.
Alternatively programmer can use <bAction> or <sAction> to create
seprate copy of hash array for each object, i.e.:
bAction := {|| hb_hClone( hValue ) }
When hash array contains symbol item (@funcName()) then when it's
executed by OLE object message it's possible to access the hash
array bound with given OLE object using QSelf() function. It maybe
useful if hash array contains instance variables and programmer
wants to access them.
Please remember that using hash array which was initialized to keep
original assign order by HB_HKEEPORDER( <hAction>, .T. ) before
adding its items you can define strict message numbers (DISPIDs), i.e.:
hAction := {=>}
HB_HKEEPORDER( hAction, .T. )
hAction[ "OPEN" ] := @myole_open() // DISPID=1
hAction[ "CLOSE" ] := @myole_close() // DISPID=2
hAction[ "SAVE" ] := @myole_save() // DISPID=3
hAction[ "LOAD" ] := @myole_load() // DISPID=4
hAction[ "PRINT" ] := @myole_print() // DISPID=5
(see example in olesrv2.prg)
best regards,
Przemek
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