Performance Build ================= {{#include ../../links.md}} Some features are for performance. For example, using [`only_i32`] or [`only_i64`] disables all other integer types (such as `u16`). Use Only One Integer Type ------------------------ If only a single integer type is needed in scripts - most of the time this is the case - it is best to avoid registering lots of functions related to other integer types that will never be used. As a result, [`Engine`] creation will be faster because fewer functions need to be loaded. The [`only_i32`] and [`only_i64`] features disable all integer types except `i32` or `i64` respectively. Use Only 32-Bit Numbers ---------------------- If only 32-bit integers are needed - again, most of the time this is the case - turn on [`only_i32`]. Under this feature, only `i32` is supported as a built-in integer type and no others. On 64-bit targets this may not gain much, but on certain 32-bit targets this improves performance due to 64-bit arithmetic requiring more CPU cycles to complete. Minimize Size of `Dynamic` ------------------------- Turning on [`no_float`] and [`only_i32`] on 32-bit targets makes the critical [`Dynamic`] data type only 8 bytes long. Normally [`Dynamic`] can be up to 16 bytes (e.g. on x86/x64 CPU's) in order to hold an `i64` or `f64`. A small [`Dynamic`] helps performance due to better cache efficiency. Use `ImmutableString` -------------------- Internally, Rhai uses _immutable_ [strings] instead of the Rust `String` type. This is mainly to avoid excessive cloning when passing function arguments. Rhai's internal string type is `ImmutableString` (basically `Rc` or `Arc` depending on the [`sync`] feature). It is cheap to clone, but expensive to modify (a new copy of the string must be made in order to change it). Therefore, functions taking `String` parameters should use `ImmutableString` or `&str` (both map to `ImmutableString`) for the best performance with Rhai. Disable Closures ---------------- Support for [closures] that capture shared variables adds material overhead to script evaluation. This is because every data access must be checked whether it is a shared value and, if so, take a read lock before reading it. Use [`no_closure`] to disable closure and capturing support to optimize the hot path because there is no need to take locks for shared data.