LocusTypeScript is a fork of TypeScript, introducing a new concept called ``locus types''.
LocusTypeScript aims to tackle exactly one problem in TypeScript, giving an appropriate type to objects that are under construction or extension:
var conn = new Connection();
conn.player = player; // New field
conn.sendName = function() { // New field
this.send(this.player.name);
};
This sort of dynamic object extension is very common in JavaScript. However, in TypeScript, conn would be inferred to be of type Connection, which lacks our new fields. We would have to create a new type with these fields, and cast the new Connection object unsafely, and keep the type in sync with any new assignments. As an additional pain-point, TypeScript will allow the fields then to be used before they are actually assigned.
Locus types allow programmers to solve these problems with an on-the-spot type creation keyword:
var conn: declare PlayerConnection = new Connection();
conn.player = player;
conn.sendName = function() {
this.send(this.player.name);
};
Now, PlayerConnection is the type that conn has after construction, containing members determined by analysis of assignment operations. The assignments may occur within loops and other control structures, in which case a type is computed from the union of all possible types. (Note: LocusTypeScript does not attempt to eliminate branches that cant actually occur, as this can get very complex without clear gain.)
As well, LocusTypeScript can improve on the case where we externally specify a PlayerConnection interface, correctly determining if fields are used before assignment:
var conn: becomes PlayerConnection = new Connection();
// If our type was simply 'PlayerConnection', we would require a cast and the following would be allowed:
var playerName = conn.player.name;
// With the 'becomes' keyword, this is an error unless 'conn.player' is assigned with the appropriate type.
In order to build the TypeScript compiler, ensure that you have Git and Node.js installed.
Clone a copy of the repo:
git clone https://github.com/ludamad/LocusTypeScript
Change to the LocusTypeScript directory:
cd LocusTypeScript
Install Jake tools and dev dependencies:
npm install -g jake
npm install
Use one of the following to build and test:
jake local # Build the compiler into built/local
jake clean # Delete the built compiler
``
## Usage
```shell
node built/local/tsc.js hello.ts