Add table.filter

src/ltablib.cpp

@@ -476,10 +476,48 @@ static int tcontains(lua_State* L) {
 }
 
 
+static int tfilter(lua_State *L) {
+  luaL_checktype(L, 1, LUA_TTABLE);
+  luaL_checktype(L, 2, LUA_TFUNCTION);
+
+  lua_newtable(L);
+  lua_Integer idx = 1;
+  lua_pushvalue(L, 1);
+  lua_pushnil(L);
+  /* stack now: out, in, key */
+  while (lua_next(L, -2)) {
+    /* stack now: out, in, key, value */
+    lua_pushvalue(L, 2);
+    lua_pushvalue(L, -2);
+    /* stack now: out, in, key, value, function, value */
+    lua_call(L, 1, 1);
+    /* stack now: out, in, key, value, bKeep */
+    const bool bKeep = lua_toboolean(L, -1);
+    lua_pop(L, 1);
+    /* stack now: out, in, key, value */
+    if (bKeep) {
+      lua_pushinteger(L, idx++);
+      /* stack now: out, in, key, value, idx */
+      lua_pushvalue(L, -2);
+      /* stack now: out, in, key, value, idx, value */
+      lua_settable(L, -6);
+      /* stack now: out, in, key, value */
+    }
+    lua_pop(L, 1);
+    /* stack now: out, in, key */
+  }
+  /* stack now: out, in */
+  lua_pop(L, 1);
+  /* stack now: out */
+  return 1;
+}
+
+
 /* }====================================================== */
 
 
 static const luaL_Reg tab_funcs[] = {
+  {"filter", tfilter},
   {"foreach", foreach},
   {"contains", tcontains},
 #ifndef PLUTO_DISABLE_TABLE_FREEZING

tests/basic.pluto

@@ -756,6 +756,13 @@ do
     assert(string.lower("HELLO", -2) == "HELlO")
     assert(string.lower("HELLO", -14) == "HELLO")
 end
+do
+    local t = { 5, 4, 3, 2, 1 }
+    t = table.filter(t, |x| -> x % 2 ~= 0)
+    assert(t[1] == 5)
+    assert(t[2] == 3)
+    assert(t[3] == 1)
+end
 
 print "Testing default table metatable."
 do