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Update compatibility.md (#1059)

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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.
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Arseny Kapoulkine 2023-10-03 07:39:48 -07:00 • committed by GitHub
parent 2a3a030341
commit 225a4a0870
Signed by: DevComp
GPG key ID: 4AEE18F83AFDEB23
1 changed files with 3 additions and 2 deletions
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docs/_pages/compatibility.md
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@ -57,7 +57,7 @@ Sandboxing challenges are [covered in the dedicated section](sandbox).
| tables honor the `__len` metamethod | ✔️ | | | tables honor the `__len` metamethod | ✔️ | |
| hex and `\z` escapes in strings | ✔️ | | | hex and `\z` escapes in strings | ✔️ | |
| support for hexadecimal floats | 🤷‍♀️ | no strong use cases | | 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++ | | 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 | | `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` | ✔️ | | | 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` | ✔️ | | | new function `table.move` | ✔️ | |
| `collectgarbage("count")` now returns only one result | ✔️ | | | `collectgarbage("count")` now returns only one result | ✔️ | |
| `coroutine.isyieldable` | ✔️ | | | `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. 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.