rhai/RELEASES.md
2020-05-20 00:06:07 +08:00

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Rhai Release Notes
==================
Version 0.14.2
==============
Regression
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* Do not optimize script with `eval_expression` - it is assumed to be one-off and short.
New features
------------
* Set limits on maximum level of nesting expressions and statements to avoid panics during parsing.
Version 0.14.1
==============
The major features for this release is modules, script resource limits, and speed improvements
(mainly due to avoiding allocations).
New features
------------
* Modules and _module resolvers_ allow loading external scripts under a module namespace.
A module can contain constant variables, Rust functions and Rhai functions.
* `export` variables and `private` functions.
* _Indexers_ for Rust types.
* Track script evaluation progress and terminate script run.
* Set limit on maximum number of operations allowed per script run.
* Set limit on maximum number of modules loaded per script run.
* A new API, `Engine::compile_scripts_with_scope`, can compile a list of script segments without needing to
first concatenate them together into one large string.
* Stepped `range` function with a custom step.
Speed improvements
------------------
### `StaticVec`
A script contains many lists - statements in a block, arguments to a function call etc.
In a typical script, most of these lists tend to be short - e.g. the vast majority of function calls contain
fewer than 4 arguments, while most statement blocks have fewer than 4-5 statements, with one or two being
the most common. Before, dynamic `Vec`'s are used to hold these short lists for very brief periods of time,
causing allocations churn.
In this version, large amounts of allocations are avoided by converting to a `StaticVec` -
a list type based on a static array for a small number of items (currently four) -
wherever possible plus other tricks. Most real-life scripts should see material speed increases.
### Pre-computed variable lookups
Almost all variable lookups, as well as lookups in loaded modules, are now pre-computed.
A variable's name is almost never used to search for the variable in the current scope.
_Getters_ and _setter_ function names are also pre-computed and cached, so no string allocations are
performed during a property get/set call.
### Pre-computed function call hashes
Lookup of all function calls, including Rust and Rhai ones, are now through pre-computed hashes.
The function name is no longer used to search for a function, making function call dispatches
much faster.
### Large Boxes for expressions and statements
The expression (`Expr`) and statement (`Stmt`) types are modified so that all of the variants contain only
one single `Box` to a large allocated structure containing _all_ the fields. This makes the `Expr` and
`Stmt` types very small (only one single pointer) and improves evaluation speed due to cache efficiency.
Error handling
--------------
Previously, when an error occurs inside a function call, the error position reported is the function
call site. This makes it difficult to diagnose the actual location of the error within the function.
A new error variant `EvalAltResult::ErrorInFunctionCall` is added in this version.
It wraps the internal error returned by the called function, including the error position within the function.