Binding properties pattern

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The binding properties pattern is combining multiple observers to force properties in different objects to be synchronized or coordinated in some way. This pattern was first described as a technique by Victor Porton.^[1][2] This pattern comes under concurrency patterns.

As an alternative to the aspect-oriented implementation of mutual properties, property binding can be proposed. In LibPropC++ C++ library it is implemented too.^[3]

Some weakness in the LibPropC++ (with property binding):

1. Its use is not transparent as it requires to be declared necessary object attributes as properties and appropriate accessor methods must be provided
2. Binding of attributes in LibPropC++ is not designed to replace method calls
3. The library does not maintain an interaction history.^[3]

There are two types of binding. One-way binding should be applied when one of the properties is read-only. In other cases, two-way binding must be applied.^[2][3]

Infinite loops can be eliminated by blocking the signal, or comparing the assigned value with the property value before assignment, or eliminating unnecessary assignments.^[2][3]

Binding properties of different types can be achieved through type conversions.^[2][3]

Binding properties with transformations can be achieved through reducing the transformation function to the problem of binding properties, and the function can be imaginary consider as Type Conversions.^[2][3]

^[2]

Properties are being kept synchronized automatically. Between library calls they always have the values expressed by the EqualityConstraints.^[3]

Property changes watching mechanism acquires some resources.^[3]

Code sketch for one-way binding may look like as follows:

import java.util.Map;
import javafx.util.Pair;

void bindMultipleOneWay(Pair<X, Y> src, Map<X, Y> dst) {
    for (Map.Entry<X, Y> pair : dst.entrySet()) {
        bindPropertiesOneWay(src.getKey(), src.getValue(), pair.getKey(), pair.getValue());
    }
}

^[2]

Two-way binding can be expressed as follows:

void bindTwoWay(X prop1, X prop2) {
    bind(prop1, prop2);
    bind(prop2, prop1);
}

^[3]

Accomplishing the binding (i.e. connecting the property change notification in an event handler) may be like as follows:

void onPropertyChange(X src, X dst) {
    blockSignal(src, onPropertyChange);
    dst = src;
    unblockSignal(src, onPropertyChange);
}

^[3]

• Software design pattern