Ecosyste.ms: Awesome
An open API service indexing awesome lists of open source software.
https://github.com/guillep/observableslots
Pharo language extension to have slots that announce changes
https://github.com/guillep/observableslots
Last synced: 16 days ago
JSON representation
Pharo language extension to have slots that announce changes
- Host: GitHub
- URL: https://github.com/guillep/observableslots
- Owner: guillep
- Created: 2019-02-11T13:10:06.000Z (almost 6 years ago)
- Default Branch: master
- Last Pushed: 2019-02-15T18:02:49.000Z (almost 6 years ago)
- Last Synced: 2024-10-31T06:42:05.254Z (2 months ago)
- Language: Smalltalk
- Size: 14.6 KB
- Stars: 5
- Watchers: 4
- Forks: 1
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# ObservableSlots
Pharo language extension to have slots that announce changes
# Installation
Execute the following lines in a playground:
```smalltalk
Metacello new
baseline: 'ObservableSlot';
repository: 'github://guillep/ObservableSlots/src';
load.
```
# Usage
## Defining Observable Slots
Once the package is loaded, you will be able to create new classes with observable slots like this:
```smalltalk
Object subclass: #ObservablePoint
slots: { #x => ObservableSlot.
#y }
classVariables: { }
package: 'ObservableSlot'
```
An observable slot works like a normal slot, and hides completely the announcement mechanism that is behind:
```smalltalk
"Create Accessors"
ObservablePoint >> x: aNumber [
x := aNumber
].
ObservablePoint >> x [
^ x
].
"Create an observable point and use it normally"
point := ObservablePoint new.
point x: 17.
self assert: point x equals: 17.
```
## Subscribing to Slots Changes
To subscribe to the ObservableSlot changes, your object can use the `TObservable` trait, that contains some methods for subscription and explicit notification.
```smalltalk
Object subclass: #ObservablePoint
uses: TObservable
slots: { #x => ObservableSlot.
#y }
classVariables: { }
package: 'ObservableSlot'
```
Then we can subscribe to it doing
```smalltalk
"Create an observable point and use it normally"
point property: #x whenChangedDo: [ "your code" ].
```
The method `property:whenChangedDo:` receives as first argument the name of the instance variable (as a symbol) and as second argument a block.
The block has either a single parameter (where it will be passed the value that has just changed) or no parameter at all.
## Manually Announce Slots Changes
Sometimes we want to have control on the announcements and manually announce that a value changed.
For example, imagine a (not so) more complex graph like:
```
abObservablePoint -- x (observable) --> someObject -- someOtherInstVar (non-observable) --> someOtherObject
```
If `someObject` has its `someOtherInstVar` changed, we could want to announce that `x` changed too.
That could be done by doing:
```smalltalk
point notifyPropertyChanged: #x.
```
## Exceptions
If the property we want to subscribe or notify to does not exist a `SlotNotFound` will be risen.
If the property exists but is not observable a `NonObservableSlotError` will be risen.
# Implementation Details
This implementation uses a `ValueHolder` to capture changes, and Slots to intercept reading and writing.