Strict Variables Mode

By default, Rhai looks up access to variables from the enclosing block scope, working its way outwards until it reaches the top (global) level, then it searches the Scope (if any) that is passed into the Engine::eval_with_scope call.

Setting Engine::set_strict_variables to true turns on Strict Variables Mode, which requires that:

• all variables/constants be defined within the same script before use, or they must be variables/constants within the provided Scope (if any),
• modules must be imported, also within the same script, before use.

Within Strict Variables mode, any attempt to access a variable or module before definition/import results in a parse error.

This way, variable access errors (usually typos) are caught during compile time instead of runtime.

let x = 42;

let y = x * z;          // <- parse error under strict variables mode:
                        //    variable 'z' is not yet defined

let z = x + w;          // <- parse error under strict variables mode:
                        //    variable 'w' is undefined

foo::bar::baz();        // <- parse error under strict variables mode:
                        //    module 'foo' is not yet defined

fn test1() {
    foo::bar::baz();    // <- parse error under strict variables mode:
                        //    module 'foo' is defined
}

import "my_module" as foo;

foo::bar::baz();        // ok!

print(foo::xyz);        // ok!

let x = abc::def;       // <- parse error under strict variables mode:
                        //    module 'abc' is undefined

fn test2() {
    foo:bar::baz();     // ok!
}