Add subject signal (#4)

Add a signal that execute functions when they connect with the most
recent value (and also with the next fired values)

Author: jeparlefrancais

.vscode/settings.json

@@ -1,5 +1,6 @@
 {
     "luau-lsp.require.directoryAliases": {
         "@pkg": "node_modules/.luau-aliases"
-    }
+    },
+    "stylua.targetReleaseVersion": "v2.0.1"
 }

CHANGELOG.md

@@ -1,5 +1,7 @@
 # Changelog
 
+- add new signal kind that fires with the last fired value ([#4](https://github.com/seaofvoices/luau-signal/pull/4))
+
 ## 0.1.1
 
 - use `luau-task` package to make Signal compatible with [Lune](https://github.com/lune-org/lune) ([#1](https://github.com/seaofvoices/luau-signal/pull/1))

README.md

@@ -4,7 +4,12 @@ A typed Luau signal library.
 
 Signals are a lightweight communication mechanism used to facilitate the exchange of information between different components or modules of a software system. Signals allow parts of a program to notify others without having a dependency on them. This decoupled approach promotes modularity, making it easier to manage and maintain complex systems by broadcasting data in messages without requiring direct knowledge of their recipients.
 
-# Installation
+This library contains two kind of signals:
+
+- `Signal.new()`: a typical signal that you can connect to and fire values
+- `Signal.newSubject(...)`: a signal that execute functions when they connect with the most recent value (and also with the next fired values)
+
+## Installation
 
 Add `luau-signal` in your dependencies:
 
@@ -48,6 +53,10 @@ connection:disconnect()
 
 Creates a new signal instance.
 
+### `Signal.newSubject<T...>(...: T...): Signal<T...>`
+
+Creates a new signal instance, except that when connecting to the signal, the callback will be immediately called with the most recent value. The arguments given to `newSubject` are the initial values that will be passed to function when they connect before anything was fire on the signal.
+
 ### `Signal:fire<T...>(...: T...)`
 
 Fires the signal, triggering all connected callback functions with the provided arguments.

foreman.toml

@@ -1,7 +1,7 @@
 [tools]
 rojo = { github = "rojo-rbx/rojo", version = "=7.4.4"}
 selene = { github = "Kampfkarren/selene", version = "=0.27.1"}
-stylua = { github = "JohnnyMorganz/styLua", version = "=0.19.1" }
-darklua = { github = "seaofvoices/darklua", version = "=0.13.1"}
-luau-lsp = { github = "JohnnyMorganz/luau-lsp", version = "=1.32.4"}
+stylua = { github = "JohnnyMorganz/styLua", version = "=2.0.1" }
+darklua = { github = "seaofvoices/darklua", version = "=0.14.0"}
+luau-lsp = { github = "JohnnyMorganz/luau-lsp", version = "=1.35.0"}
 wally = { github = "UpliftGames/wally", version = "=0.3.2" }

package.json

@@ -22,7 +22,8 @@
     "lint": "sh ./scripts/analyze.sh",
     "format": "stylua .",
     "style-check": "stylua . --check",
-    "clean": "rm -rf node_modules roblox build"
+    "clean": "rm -rf node_modules roblox build",
+    "verify-pack": "yarn pack --dry-run"
   },
   "dependencies": {
     "luau-task": "^1.0.1"

src/Signal.lua

@@ -3,6 +3,10 @@ local task = require('@pkg/luau-task')
 local Connection = require('./Connection')
 export type Connection = Connection.Connection
 
+export type ConnectableSignal<T...> = {
+    connect: (self: ConnectableSignal<T...>, callback: (T...) -> ()) -> Connection,
+}
+
 export type Signal<T...> = {
     fire: (self: Signal<T...>, T...) -> (),
     connect: (self: Signal<T...>, callback: (T...) -> ()) -> Connection,

src/Subject.lua

@@ -0,0 +1,54 @@
+local task = require('@pkg/luau-task')
+
+local Connection = require('./Connection')
+local Signal = require('./Signal')
+
+type Connection = Connection.Connection
+
+export type Subject<T...> = Signal.Signal<T...>
+
+type Private<T...> = {
+    _last: { any },
+    _lastLength: number,
+}
+type PrivateSubject<T...> = Subject<T...> & Private<T...>
+
+type SubjectStatic = {
+    new: <T...>(T...) -> Subject<T...>,
+
+    fire: <T...>(self: Subject<T...>, T...) -> (),
+    connect: <T...>(self: Subject<T...>, callback: (T...) -> ()) -> Connection,
+}
+
+local Subject: SubjectStatic = setmetatable({}, { __index = Signal }) :: any
+local SubjectMetatable = {
+    __index = Subject,
+}
+
+function Subject.new<T...>(...): Subject<T...>
+    local self: Private<T...> = Signal.new() :: any
+
+    self._last = { ... }
+    self._lastLength = select('#', ...)
+
+    return setmetatable(self, SubjectMetatable) :: any
+end
+
+function Subject:fire<T...>(...)
+    local self: PrivateSubject<T...> = self :: any
+
+    self._last = { ... }
+    self._lastLength = select('#', ...)
+
+    Signal.fire(self :: any, ...)
+end
+
+function Subject:connect<T...>(callback: (T...) -> ()): Connection
+    local self: PrivateSubject<T...> = self :: any
+
+    task.spawn(callback, unpack(self._last, 1, self._lastLength))
+
+    return Signal.connect(self :: any, callback)
+end
+
+return Subject

src/init.lua

@@ -1,7 +1,12 @@
 local Connection = require('./Connection')
 local Signal = require('./Signal')
+local Subject = require('./Subject')
 
 export type Connection = Connection.Connection
 export type Signal<T...> = Signal.Signal<T...>
+export type ConnectableSignal<T...> = Signal.ConnectableSignal<T...>
 
-return Signal
+return {
+    new = Signal.new,
+    newSubject = Subject.new,
+}