From 225a4a08702f39163ad09d2d9af858bef46c87cc Mon Sep 17 00:00:00 2001 From: Arseny Kapoulkine Date: Tue, 3 Oct 2023 07:39:48 -0700 Subject: [PATCH] Update compatibility.md (#1059) Add a note about Lua 5.3 change to semantics of __eq metamethod. We currently do not plan to implement this as this breaks backwards compatibility and makes these operators harder to reason about from the type checking perspective. Fixes #1051. --- docs/_pages/compatibility.md | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/docs/_pages/compatibility.md b/docs/_pages/compatibility.md index 94f8809b..1b2c83ef 100644 --- a/docs/_pages/compatibility.md +++ b/docs/_pages/compatibility.md @@ -57,7 +57,7 @@ Sandboxing challenges are [covered in the dedicated section](sandbox). | tables honor the `__len` metamethod | ✔️ | | | hex and `\z` escapes in strings | ✔️ | | | support for hexadecimal floats | 🤷‍♀️ | no strong use cases | -| order metamethods work for different types | ❌ | no strong use cases and more complicated semantics, compatibility and performance implications | +| order metamethods (`__lt`/`__le`) are called for unrelated metatables | ❌ | no strong use cases and more complicated semantics, compatibility and performance implications | | empty statement | 🤷‍♀️ | less useful in Lua than in JS/C#/C/C++ | | `break` statement may appear in the middle of a block | 🤷‍♀️ | we'd like to do it consistently for `break`/`return`/`continue` but there be dragons | | arguments for function called through `xpcall` | ✔️ | | @@ -92,7 +92,8 @@ Ephemeron tables may be implemented at some point since they do have valid uses | new function `table.move` | ✔️ | | | `collectgarbage("count")` now returns only one result | ✔️ | | | `coroutine.isyieldable` | ✔️ | | -| stricter error checking for `table.insert`/`table.remove` | 😞 | we love this, but it breaks compatibility +| stricter error checking for `table.insert`/`table.remove` | 😞 | we love this, but it breaks compatibility | +| `__eq` metamethod is called for unrelated metatables | ❌ | backwards compatibility and typechecking implications | It's important to highlight integer support and bitwise operators. For Luau, it's rare that a full 64-bit integer type is necessary - double-precision types support integers up to 2^53 (in Lua which is used in embedded space, integers may be more appealing in environments without a native 64-bit FPU). However, there's a *lot* of value in having a single number type, both from performance perspective and for consistency. Notably, Lua doesn't handle integer overflow properly, so using integers also carries compatibility implications.