mirror of
https://gerrit.wikimedia.org/r/mediawiki/extensions/Popups
synced 2024-12-20 11:10:40 +00:00
69 lines
3.2 KiB
Markdown
69 lines
3.2 KiB
Markdown
|
# 6. Factories
|
|||
|
|
|
|||
|
|
Date: 08/11/2016
|
|||
|
|
|
|||
|
|
## Status
|
|||
|
|
|
|||
|
|
Accepted.
|
|||
|
|
|
|||
|
|
This ADR was accepted implicitly by the (current) primary maintainer of this
|
|||
|
|
repository, Sam Smith. The date of this ADR was changed to reflect this.
|
|||
|
|
|
|||
|
|
## Context
|
|||
|
|
|
|||
|
|
Given that the majority of the codebase is going to be rewritten, there's
|
|||
|
|
a need for a consistent style for building the system anew.
|
|||
|
|
|
|||
|
|
The [Reading Web team](https://www.mediawiki.org/wiki/Reading/Web/Team),
|
|||
|
|
historically, has tended towards taking an object oriented approach to building
|
|||
|
|
software. However, a typical result of this approach are classes that have many
|
|||
|
|
varied concerns, share – not specialise – behaviour via inheritance rather than
|
|||
|
|
via composition. These issues are evidenced by a lack of unit tests, i.e. the
|
|||
|
|
classes become increasingly hard to test and even harder to test in isolation
|
|||
|
|
to the point where high-level integration tests are relied on for validation of
|
|||
|
|
the design.
|
|||
|
|
|
|||
|
|
Unless attention is paid, these classes have all of their members exposed by
|
|||
|
|
default due to a lack of support for visibility modifiers from either the
|
|||
|
|
JavaScript language or our (current) tooling. Like other teams, the [Reading
|
|||
|
|
Web team](https://www.mediawiki.org/wiki/Reading/Web/Team) tends to follow the
|
|||
|
|
convention of prefixing private member names with an underscore.
|
|||
|
|
|
|||
|
|
Moreover, while planning the rewrite of the codebase, [the decision to use
|
|||
|
|
Redux to maintain state](./0002-contain-and-manage-state.md) was made very
|
|||
|
|
early on. A significant part of the codebase will be written in the style that
|
|||
|
|
Redux requires: functions that return objects, or _factories_.
|
|||
|
|
|
|||
|
|
What's needed, then, is a general rule that, when applied, leads the Reading
|
|||
|
|
Web team to produce a codebase that's easier to maintain (verify and modify)
|
|||
|
|
and is familiar. This rule must also acknowledge that it must be broken now and
|
|||
|
|
again.
|
|||
|
|
|
|||
|
|
## Decision
|
|||
|
|
|
|||
|
|
1. Favour factories over classes – however we wish to define them, e.g. with
|
|||
|
|
[OOjs](https://www.mediawiki.org/wiki/OOjs) – by default.
|
|||
|
|
2. Favour classes when the performance benefits of prototypal inheritance far
|
|||
|
|
outweigh the benefits of consistency and simplicity.
|
|||
|
|
|
|||
|
|
## Consequences
|
|||
|
|
|
|||
|
|
The most obvious consequence of this decision is the easy portability of the
|
|||
|
|
codebase: there's no requirement for a framework to help define classes and
|
|||
|
|
manage inheritance, e.g. [OOjs](https://www.mediawiki.org/wiki/OOjs). Moreover,
|
|||
|
|
the `new` operator in `new Foo()`, is simply replaced with the `createFoo`
|
|||
|
|
factory function, and the `instanceof` operator is rendered useless.
|
|||
|
|
|
|||
|
|
The more subtle consequence is that behaviour must be shared via composition
|
|||
|
|
since the use of inheritance is strongly discouraged. The most important
|
|||
|
|
positive consequence of this is is that the system will be more flexible as
|
|||
|
|
it'll be composed of implementations of small interfaces. The most important
|
|||
|
|
negative consequence is that more effort will be required when sharing
|
|||
|
|
behaviour between parts of the system, which is trivial using inheritance, as
|
|||
|
|
attention must be paid when designing these interfaces.
|
|||
|
|
|
|||
|
|
Despite being the negative consequence, requiring more attention to be paid
|
|||
|
|
when defining behaviour should make it harder to write – and easier to spot
|
|||
|
|
– components "that have many varied concerns" and, hopefully, result in
|
|||
|
|
components that are easier to test.
|