Lua: table.select API

client/space_lua/stdlib/table.ts

@@ -11,7 +11,7 @@ import {
   type LuaValue,
   luaValueToJS,
 } from "../runtime.ts";
-import { asyncQuickSort } from "../util.ts";
+import { asyncQuickSort, evalPromiseValues } from "../util.ts";
 
 export const tableApi = new LuaTable({
   /**
@@ -99,6 +99,7 @@ export const tableApi = new LuaTable({
   ),
   /**
    * Returns the keys of a table.
+   * Note: Space Lua specific
    * @param tbl - The table to get the keys from.
    * @returns The keys of the table.
    */
@@ -111,6 +112,7 @@ export const tableApi = new LuaTable({
   }),
   /**
    * Checks if a table (used as an array) contains a value.
+   * Note: Space Lua specific
    * @param tbl - The table to check.
    * @param value - The value to check for.
    * @returns True if the value is in the table, false otherwise.
@@ -138,6 +140,34 @@ export const tableApi = new LuaTable({
       }
     },
   ),
+  /**
+   * Returns a new table from an old one, only with selected keys
+   * @param tbl a Lua table or JS object
+   * @param keys a list of keys to select from the table, if keys[0] is a table or array, assumed to contain the keys to select
+   * @returns a new table with only the selected keys
+   */
+  select: new LuaBuiltinFunction(
+    (sf, tbl: LuaTable | Record<string, any>, ...keys: LuaValue[]) => {
+      // Normalize arguments
+      if (Array.isArray(keys[0])) {
+        // First argument is key array, let's unpack
+        keys = keys[0];
+      } else if (keys[0] instanceof LuaTable) {
+        keys = keys[0].toJSArray();
+      }
+      const resultTable = new LuaTable();
+      const setPromises: (void | Promise<void>)[] = [];
+      for (const key of keys) {
+        setPromises.push(resultTable.set(key, luaGet(tbl, key, null, sf)));
+      }
+      const promised = evalPromiseValues(setPromises);
+      if (promised instanceof Promise) {
+        return promised.then(() => resultTable);
+      } else {
+        return resultTable;
+      }
+    },
+  ),
   pack: new LuaBuiltinFunction((_sf, ...args: any[]) => {
     const tbl = new LuaTable();
     for (let i = 0; i < args.length; i++) {

client/space_lua/stdlib/table_test.lua

@@ -1,9 +1,37 @@
+function deepCompare(t1, t2)
+    if t1 == t2 then return true end
+    -- If they are the same object, return true
+    if type(t1) ~= "table" or type(t2) ~= "table" then return false end
+    -- If not both tables, return false
+    -- Check if both tables have the same number of keys
+    local t1_keys = 0
+    local t2_keys = 0
+    for k in pairs(t1) do
+        t1_keys = t1_keys + 1
+    end
+    for k in pairs(t2) do
+        t2_keys = t2_keys + 1
+    end
+    if t1_keys ~= t2_keys then return false end
+
+    -- Recursively compare each key-value pair
+    for k, v in pairs(t1) do
+        if not deepCompare(v, t2[k]) then
+            return false
+        end
+    end
+
+    return true
+end
+
 local function assertEqual(a, b)
-    if a ~= b then
-        error("Assertion failed: " .. a .. " is not equal to " .. b)
+    if not deepCompare(a, b) then
+        error("Assertion failed: " .. tostring(a) .. " is not equal to " .. tostring(b))
     end
 end
 
+
+
 -- Basic table operations
 local t = { 1, 2, 3 }
 table.insert(t, 4)
@@ -155,3 +183,10 @@ local idx, two = table.find(t, function(v) return v == 2 end)
 assertEqual(idx, 3)
 assertEqual(two, 2)
 assertEqual(table.find(t, function(v) return v == 4 end), nil)
+
+-- Test table.select
+local tbl = {name = "Pete", age = 100, parents = {"John", "Jane"}}
+assertEqual(table.select(tbl, "name"), {name = "Pete"})
+assertEqual(table.select(tbl, {"name"}), {name = "Pete"})
+assertEqual(table.select(tbl, "name", "age"), { name = "Pete", age = 100})
+assertEqual(table.select(tbl, "name", "age", "non-existing"), { name = "Pete", age = 100})