rhai/RELEASES.md

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Rhai Release Notes
==================
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Version 0.14.2
==============
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Regression fix
--------------
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* Do not optimize script with `eval_expression` - it is assumed to be one-off and short.
Bug fixes
---------
* Indexing with an index or dot expression now works property (it compiled wrongly before).
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For example, `let s = "hello"; s[s.len-1] = 'x';` now works property instead of causing a runtime error.
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Breaking changes
----------------
* `Engine::compile_XXX` functions now return `ParseError` instead of `Box<ParseError>`.
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* The `RegisterDynamicFn` trait is merged into the `RegisterResultFn` trait which now always returns
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`Result<Dynamic, Box<EvalAltResult>>`.
* Default maximum limit on levels of nested function calls is fine-tuned and set to a different value.
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* Some operator functions are now built in (see _Speed enhancements_ below), so they are available even
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under `Engine::new_raw`.
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* Strings are now immutable. The type `rhai::ImmutableString` is used instead of `std::string::String`.
This is to avoid excessive cloning of strings. All native-Rust functions taking string parameters
should switch to `rhai::ImmutableString` (which is either `Rc<String>` or `Arc<String>` depending on
whether the `sync` feature is used).
* Native Rust functions registered with the `Engine` also mutates the first argument when called in
normal function-call style (previously the first argument will be passed by _value_ if not called
in method-call style). Of course, if the first argument is a calculated value (e.g. result of an
expression), then mutating it has no effect, but at least it is not cloned.
* Some built-in methods (e.g. `len` for string, `floor` for `FLOAT`) now have _property_ versions in
addition to methods to simplify coding.
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New features
------------
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* Set limit on maximum level of nesting expressions and statements to avoid panics during parsing.
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* New `EvalPackage` to disable `eval`.
* `Module::set_getter_fn`, `Module::set_setter_fn` and `Module:set_indexer_fn` to register getter/setter/indexer functions.
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* `Engine::call_fn_dynamic` for more control in calling script functions.
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Speed enhancements
------------------
* Common operators (e.g. `+`, `>`, `==`) now call into highly efficient built-in implementations for standard types
(i.e. `INT`, `FLOAT`, `bool`, `char`, `()` and `ImmutableString`) if not overridden by a registered function.
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This yields a 5-10% speed benefit depending on script operator usage. Scripts running tight loops will see
significant speed-up.
* Common assignment operators (e.g. `+=`, `%=`) now call into highly efficient built-in implementations for
standard types (i.e. `INT`, `FLOAT`, `bool`, `char`, `()` and `ImmutableString`) if not overridden by a registered function.
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* Implementations of common operators for standard types are removed from the `ArithmeticPackage` and `LogicPackage`
(and therefore the `CorePackage`) because they are now always available, even under `Engine::new_raw`.
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* Operator-assignment statements (e.g. `+=`) are now handled directly and much faster.
* Strings are now _immutable_ and use the `rhai::ImmutableString` type, eliminating large amounts of cloning.
* For Native Rust functions taking a first `&mut` parameter, the first argument is passed by reference instead of
by value, even if not called in method-call style. This allows many functions declared with `&mut` parameter to avoid
excessive cloning. For example, if `a` is a large array, getting its length in this manner: `len(a)` used to result
in a full clone of `a` before taking the length and throwing the copy away. Now, `a` is simply passed by reference,
avoiding the cloning altogether.
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* A custom hasher simply passes through `u64` keys without hashing to avoid function call hash keys
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(which are by themselves `u64`) being hashed twice.
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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.