问题
I am trying to create an extremely simple Vector class as a subclass of Array in Smalltalk. My code to create the class looks like this:
Array subclass: #Vector
Vector comment: 'I represent a Vector of integers'
Vector class extend [
new [
| r |
<category: 'instance creation'>
r := super new.
r init.
^r
]
]
Vector extend [
init [
<category: 'initialization'>
]
]
Obviously I haven't written any methods yet, but I'm just trying to get this part working first. After the class is created as above, if I type: v := Vector new: 4 I get error:
Object: Vector error: should not be implemented in this class, use #new instead
SystemExceptions.WrongMessageSent(Exception)>>signal (ExcHandling.st:254)
SystemExceptions.WrongMessageSent class>>signalOn:useInstead: (SysExcept.st:1219)
Vector class(Behavior)>>new: (Builtins.st:70)
UndefinedObject>>executeStatements (a String:1)
nil
I had assumed that since it is a subclass of Array, I could create a Vector in this manner. What is the best way to go about doing this? Thanks!
Edit -- I figured it out. After reading deeper into the tutorial, I found I needed to include <shape: #pointer>
回答1:
Array is a special kind of class that has indexable instances of different lengths.
In GNU Smalltalk (which you appear to be using) the Array class is declared as:
ArrayedCollection subclass: Array [
<shape: #pointer>
To inherit this behaviour you can use:
Array subclass: Vector [<shape: #inherit>]
But in most cases it makes more sense to make a class that encapsulate an Array rather than a class that inherits from Array.
It's also worth pointing out that OrderedCollection
is the Smalltalk equivalent of the vector container from C++ and Java.
来源:https://stackoverflow.com/questions/9474268/basic-smalltalk-subclass