.DT
classes
Discworld creator help
classes
.SH Name
.SI 5
classes - A funky way of storing data
.EI
.SH Syntax
.SI 5
class [class name] {
<member type> <member name>;
...
}
class <class name> <variable name>;
.EI
.SH Description
.SP 5 5
Classes in LPC are the equivalent of a structure in C. A structure is
essentially a user-defined type, that is composed of fields or members
that can have different types.
Classes are excellent ways of storing database type data, and can be
used as an alternative to mappings. They provide a simple and intuitive
way of accessing data, and it means that you do not have to rely on array
indicies excessively.
Classes can also be used in conjunction with mappings
and arrays, and it is possible to have an array of classes or a class as
the value section of a mapping.
Classes must be initialised first with the 'new' function, this allocates
memory for them and sets its member variables to their default values. This
is usually 0. The "call_other" operator (->) can be used to access a member of
a class, returning either its value or storing a new item in it.
The sizeof() efun can be used to determine how many members are in a class,
and it is possible to place a reference to the same class inside itself. To
determine whether or not a given variable is a class, the classp() efun can
be used.
In order for a class to be used in another object, then the definition must
also be contained in that object. Otherwise the class is said to have gone
"out of scope", and its members can no longer be accessed using the "->"
operator.
Classes are saved and restored correctly by save_object()/restore_object(),
although remember if you try and save an object reference then this will be stored
as 0 in the save file. As classes are stored by reference, similar to arrays
and mappings, you should use the copy() efun when querying data of this type
to avoid accidently changing its contents.
.EP
Example
class customer_details {
int customer_id;
string customer_name;
string customer_address;
string *purchases;
class customer_details *family_members;
int total_spent;
}
Here is a completely useless function that shows how to use a class in
practice:
int create_customer() {
class customer_details customer;
customer = new(class customer_details);
customer->customer_id = 5;
customer->customer_name = "John Smith";
customer->customer->address = "123 Berryl Street\n"
"Frog Town, Womble City, 2000\n"
"Australia\n";
customer->purchases = ({ "rug", "cat food", "waffle maker" });
customer->family_members = ({ });
customer->total_spent = 100;
/* Returns 5 */
return customer->customer_id;
} /* create_customer() */
Example 2
class shoe {
string brand_name;
string shoe_name;
int us_size;
int uk_size;
int stock;
}
This function shows how to use a class to make a simple database
that stores shoe details;
class shoe *shoes = ({ });
int add_new_shoe(string shoe, string brand, int s_size) {
class shoe new_shoe;
int i, size;
if (undefinedp(shoes))
return 0;
/* Shoes is an array, look for an existing shoe of
this type. */
size = sizeof(shoes);
for (i = 0; i < size; i++) {
if (shoes[i]->shoe_name == shoe) {
shoes->stock = shoes->stock + 1;
return 1;
}
}
/* No shoe of this type... add it! */
new_shoe = new(class shoe, brand_name : brand, shoe_name : shoe,
us_size : s_size, uk_size : (s_size * 2) / 3, stock : 1);
shoes += ({ new_shoe });
return 1;
} /* add_new_shoe() */
.SH See also
.SI 5
help, new, classp, copy, sizeof
.EI
