# Eager Operator Evaluation

Most operators are actually function calls, and those functions can be overridden, so whether they are optimized away depends on the situation:

No external functions

Rhai guarantees that no external function will be run, which may trigger side-effects (unless the optimization level is `OptimizationLevel::Full`).

``````// The following is most likely generated by machine.

const DECISION = 1;             // this is an integer, one of the standard types

if DECISION == 1 {              // this is optimized into 'true'
:
} else if DECISION == 2 {       // this is optimized into 'false'
:
} else if DECISION == 3 {       // this is optimized into 'false'
:
} else {
:
}

// Or an equivalent using 'switch':

switch DECISION {
1 => ...,                   // this statement is promoted
2 => ...,                   // this statement is eliminated
3 => ...,                   // this statement is eliminated
_ => ...                    // this statement is eliminated
}
``````

## Pre-Evaluation of Constant Expressions

Because of the eager evaluation of operators for standard types, many constant expressions will be evaluated and replaced by the result.

``````let x = (1+2) * 3 - 4/5 % 6;    // will be replaced by 'let x = 9'

let y = (1 > 2) || (3 <= 4);    // will be replaced by 'let y = true'
``````

For operators that are not optimized away due to one of the above reasons, the function calls are simply left behind.

``````// Assume 'new_state' returns some custom type that is NOT one of the standard types.
// Also assume that the '==' operator is defined for that custom type.
const DECISION_1 = new_state(1);
const DECISION_2 = new_state(2);
const DECISION_3 = new_state(3);

if DECISION == 1 {              // NOT optimized away because the operator is not built-in
:                           // and may cause side-effects if called!
:
} else if DECISION == 2 {       // same here, NOT optimized away
:
} else if DECISION == 3 {       // same here, NOT optimized away
:
} else {
:
}
``````

Alternatively, turn the optimizer to `OptimizationLevel::Full`.