Predecessor

Overview

This set of libraries is intended to provide useful classes to inherit from, in a way that is cross compatible between multiple languages. A version of this library is currently available in:

• Python (2 or 3)
• Javascript

The libraries currently provide:

• singleton objects
• serializable objects

Singleton

The singleton class provides a way to ensure you only have one instance of a class. For instance:

from predecessor import Singleton


class Example(Singleton):
    def __init__(self, foo, bar):
        self.foo = foo
        self.bar = bar


a = Example(3, 8)
b = Example(2, 9)
a is b  # returns True
a.foo == b.foo == 3  # returns True

Or equivalently in Javascript:

const Singleton = require('predecessor').Singleton;

class Example extends Singleton {
    constructor(foo, bar)   {
        this.foo = foo;
        this.bar = bar;
    }
}

let a = new Example(3, 8);
let b = new Example(2, 9);
a === b;  // returns true
a.foo === 3;  // returns true
b.foo === 3;  // returns true

Serializable

The singleton class provides a way to serialize a class without needing to care about what form the resulting blob takes. If a compatible class definition is available in all supported languages, it should be deserializable in all supported languages.

The Basic Case

from predecessor import Serializable


class Example(Serializable):
    def __init__(self, foo, bar):  # Note that keyword args are not supported
        self.foo = foo
        self.bar = bar

    def serialized(self):
        return super(Example, self).serialized(self.foo, self.bar)


a = Example(3, 8)
b = Example.deserialize(a.serialized())
a.foo == b.foo == 3  # returns True
a.bar == b.bar == 8  # returns True

Or equivalently in Javascript:

const Serializable = require('predecessor').Serializable;

class Example extends Serializable {
    constructor(foo, bar)   {
        this.foo = foo;
        this.bar = bar;
    }

    serialized()    {
        return super.serialized(this.foo, this.bar);
    }
}

let a = new Example(3, 8);
let b = Example.deserialize(a.serialized());
a.foo === 3;  // returns true
b.foo === 3;  // returns true
a.foo === 8;  // returns true
b.foo === 8;  // returns true

Implied Serialization

In both languages, you can also use implied serialization. This looks like:

class Example(Serializable):
    __slots__ = ('a', 'b', 'c')

    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c

class Example extends Serializable  {
    constructor(a, b, c)    {
        super();
        this._slots = ['a', 'b', 'c'];
        this.a = a;
        this.b = b;
        this.c = c;
    }
}

Advanced Recombination

In both languages you can do data processing before feeding things into your constructor.

class Example(Serializable):
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c

    def serialized(self):
        return super(Example, self).serialized(self.a, self.b)

    @classmethod
    def recombine(cls, a, b):
        return cls(a, b, a+b)

class Example extends Serializable  {
    constructor(a, b, c)    {
        super();
        this.a = a;
        this.b = b;
        this.c = c;
    }

    serialized()    {
        return super.serialized(this.a, this.b);
    }

    static recombine(a, b)  {
        return new this(a, b, a+b);
    }
}