Volatility Considerations for Full Optimization Level

Even if a custom function does not mutate state nor cause side-effects, it may still be volatile, i.e. it depends on the external environment and is not pure.

A perfect example is a function that gets the current time – obviously each run will return a different value!

print(get_current_time(true));      // prints the current time
                                    // notice the call to 'get_current_time'
                                    // has constant arguments

// The above, under full optimization level, is rewritten to:

print("10:25AM");                   // the function call is replaced by
                                    // its result at the time of optimization!

The optimizer, when using OptimizationLevel::Full, merrily assumes that all functions are non-volatile, so when it finds constant arguments (or none) it eagerly executes the function call and replaces it with the result.

This causes the script to behave differently from the intended semantics.