Add: select

src/Lua/Standard/Basic/SelectFunction.cs

@@ -0,0 +1,37 @@
+namespace Lua.Standard.Basic;
+
+public sealed class SelectFunction : LuaFunction
+{
+    public override string Name => "select";
+    public static readonly SelectFunction Instance = new();
+
+    protected override ValueTask<int> InvokeAsyncCore(LuaFunctionExecutionContext context, Memory<LuaValue> buffer, CancellationToken cancellationToken)
+    {
+        var arg0 = context.ReadArgument(0);
+        
+        if (arg0.TryRead<double>(out var d))
+        {
+            if (!MathEx.IsInteger(d))
+            {
+                throw new LuaRuntimeException(context.State.GetTracebacks(), "bad argument #1 to 'select' (number has no integer representation)");
+            }
+
+            var index = (int)d;
+
+            var span = context.Arguments[index..];
+            span.CopyTo(buffer.Span);
+
+            return new(span.Length);
+        }
+        else if (arg0.TryRead<string>(out var str) && str == "#")
+        {
+            buffer.Span[0] = context.ArgumentCount - 1;
+            return new(1);
+        }
+        else
+        {
+            LuaRuntimeException.BadArgument(context.State.GetTracebacks(), 1, Name, "number", arg0.Type.ToString());
+            return default;
+        }
+    }
+}