Conversion Risk Policies¶
A conversion risk policy is a monovalue type that indicates how a unit conversion function should handle conversion risks. Au tracks two kinds of conversion risk: overflow and truncation. Each conversion risk policy will either enable or disable checking for each of these risks.
Conversion Risk Sets¶
A conversion risk set represents a set of risks. It may be empty, refer to an individual risk, or
refer to multiple risks. The only supported way to form a risk set is to use a built-in risk set
constant, or else to combine such constants using the bitwise-or operator (|). Here are the risk
set constants:
OVERFLOW_RISKTRUNCATION_RISKALL_RISKS- Currently, this is equivalent to
OVERFLOW_RISK | TRUNCATION_RISK. However, if we later discover new conversion risks to guard against, then this constant would change to include them too.
- Currently, this is equivalent to
Forming Policies From Sets¶
To turn a conversion risk set, RISK_SET, into a conversion risk policy, use one of two
functions:
ignore(RISK_SET)- This produces a policy that ignores all the risks in
RISK_SET, and checks for all other risks.
- This produces a policy that ignores all the risks in
check_for(RISK_SET)- This produces a policy that checks for all the risks in
RISK_SET, and ignores all other risks.
- This produces a policy that checks for all the risks in
In practice, ignore() is used very commonly, and check_for() is used very rarely, mostly
internally to the library.