Add tableext.toset (#699)

Felt like tableext should have a `toset` util.

Author: Alexander-L-Robert

lute/std/libs/tableext.luau

@@ -56,6 +56,14 @@ function tableext.keys<K, V>(tbl: { [K]: V }): { K }
 	return keys
 end
 
+function tableext.toset<T>(tbl: { T }): { [T]: true }
+	local set: { [T]: true } = {}
+	for _, v in tbl do
+		set[v] = true
+	end
+	return set
+end
+
 function tableext.reverse<T>(tbl: { T }, inplace: boolean?)
 	local new = if inplace then tbl else {}
 	local i, j = 1, #tbl

tests/std/tableext.test.luau

@@ -62,4 +62,39 @@ test.suite("TableExt", function(suite)
 		assert.tableeq(b, { 4, 5, 6 })
 		assert.tableeq(c, { 6, 5, 4 })
 	end)
+
+	suite:case("toset", function(assert)
+		local a = { 1, 2, 4, 2, 1 }
+		local setA = tableext.toset(a)
+		assert.eq(setA[1], true)
+		assert.eq(setA[2], true)
+		assert.eq(setA[3], nil)
+		assert.eq(setA[4], true)
+		assert.eq(setA[5], nil)
+
+		local setSize = #tableext.keys(setA)
+		assert.eq(setSize, 3)
+		assert.neq(setSize, #a)
+
+		-- Sanity check: sets created using an array of numbers don't break from having "gaps" between the number keys.
+
+		local foundKeys: { number } = {}
+		for key, value in setA do
+			assert.eq(value, true)
+			table.insert(foundKeys, key)
+		end
+		assert.eq(#foundKeys, setSize)
+		assert.eq(setA[foundKeys[1]], true)
+		assert.eq(setA[foundKeys[2]], true)
+		assert.eq(setA[foundKeys[3]], true)
+
+		local b = { "a", "b", "c", "a" }
+		local setB = tableext.toset(b)
+		assert.eq(setB["a"], true)
+		assert.eq(setB["b"], true)
+		assert.eq(setB["c"], true)
+		assert.eq(setB["d"], nil)
+		assert.eq(#tableext.keys(setB), 3)
+		assert.neq(#tableext.keys(setB), #b)
+	end)
 end)