record - Define and create records (similar to 'C' structures)
package require Tcl 8.2
package require struct ?1.3?
The ::struct::record package provides a mechanism to group variables together as one data structure, similar to a 'C' structure. The members of a record can be variables or other records. However, a record can not contain circular record, i.e. records that contain the same record as a member.
This package was structured so that it is very similar to how Tk objects work. Each record definition creates a record object that encompasses that definition. Subsequently, that record object can create instances of that record. These instances can then be manipulated with the cget and configure methods.
The package only contains one top level command, but several sub commands (see below). It also obeys the namespace in which the record was define, hence the objects returned are fully qualified.
Record members can either be variables, or other records, However, the same record can not be nested witin itself (circular). To define a nested record, you need to specify the record keyword, along the with name of the record, and the name of the instance of that nested record. For example, it would look like this:
# this is the nested record
record define mynestedrecord {
nest1
nest2
}
# This is the main record
record define myrecord {
mem1
mem2
{record mynestedrecord mem3}
}
|
record define myrecord {
mem1
{mem2 5}
}
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Getting Values
To get a value of a member, there are several ways to do this.
Setting Values
To set a value of a member, there are several ways to do this.
Alias access
In the original implementation, access was done by using dot notation similar to how 'C' structures are accessed. However, there was a concensus to make the interface more Tcl like, which made sense. However, the original alias access still exists. It might prove to be helpful to some.
Basically, for every member of every instance, an alias is created. This alias is used to get and set values for that member. An example will illustrate the point, using the above defined records:
# Create an instance first
% myrecord inst1
::inst1
% # To get a member of an instance, just use the
% # alias (it behaves like a Tcl command):
% inst1.mem1
%
% # To set a member via the alias, just include
% # a value (optionally the equal sign - syntactic sugar)
% inst1.mem1 = 5
5
% inst1.mem1
5
% # For nested records, just continue with the
% # dot notation (note no equal sign)
% inst1.mem3.nest1 10
10
% inst1.mem3.nest1
10
% # just the instance by itself gives all
% # member/values pairs for that instance
% inst1
-mem1 5 -mem2 {} -mem3 {-nest1 10 -nest2 {}}
% # and to get all members within the nested record
% inst1.mem3
-nest1 10 -nest2 {}
%
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The following subcommands and corresponding arguments are available to any record command:
The following subcommands and corresponding arguments are available to any record instance command:
Two examples are provided to give an good illustration on how to use this package.
Example 1
Probably the most obvious example would be to hold contact information, such as addresses, phone numbers, comments, etc. Since a person can have multiple phone numbers, multiple email addresses, etc, we will use nested records to define these. So, the first thing we do is define the nested records:
##
## This is an interactive example, to see what is
## returned by each command as well.
##
% namespace import ::struct::record::*
% # define a nested record. Notice that country has default 'USA'.
% record define locations {
street
street2
city
state
zipcode
{country USA}
phone
}
::locations
% # Define the main record. Notice that it uses the location record twice.
% record define contacts {
first
middle
last
{record locations home}
{record locations work}
}
::contacts
% # Create an instance for the contacts record.
% contacts cont1
::cont1
% # Display some introspection values
% record show records
::contacts ::locations
% #
% record show values cont1
-first {} -middle {} -last {} -home {-street {} -street2 {} -city {} -state {} -zipcode {} -country USA -phone {}} -work {-street {} -street2 {} -city {} -state {} -zipcode {} -country USA -phone {}}
% #
% record show instances contacts
::cont1
% #
% cont1 config
-first {} -middle {} -last {} -home {-street {} -street2 {} -city {} -state {} -zipcode {} -country USA -phone {}} -work {-street {} -street2 {} -city {} -state {} -zipcode {} -country USA -phone {}}
% #
% cont1 cget
-first {} -middle {} -last {} -home {-street {} -street2 {} -city {} -state {} -zipcode {} -country USA -phone {}} -work {-street {} -street2 {} -city {} -state {} -zipcode {} -country USA -phone {}}
% # copy one record to another record
% record define contacts2 [record show members contacts]
::contacts2
% record show members contacts2
first middle last {record locations home} {record locations work}
% record show members contacts
first middle last {record locations home} {record locations work}
%
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Example 1
This next example just illustrates a simple linked list
% # define a very simple record for linked list
% record define llist {
value
next
}
::llist
% llist lstart
::lstart
% lstart config -value 1 -next [llist #auto]
% [lstart cget -next] config -value 2 -next [llist #auto]
% [[lstart cget -next] cget -next] config -value 3 -next "end"
% set next lstart
lstart
% while 1 {
lappend values [$next cget -value]
set next [$next cget -next]
if {[string match "end" $next]} {break}
}
% puts "$values"
1 2 3
% # cleanup linked list
% # We could just use delete record llist also
% foreach I [record show instances llist] {
record delete instance $I
}
% record show instances llist
%
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data structures, record, struct
Copyright © 2002, Brett Schwarz <brett_schwarz@yahoo.com>