In what situations would I specify operation as unchecked?

Question

For example:

int value = Int32.MaxValue;

unchecked
{
    value += 1;
}

In what ways would this be useful? can you think of any?

Answer 1

Use unchecked when:

• You want to express a constant via overflow (this can be useful when specifying bit patterns)
• You want arithmetic to overflow without causing an error

The latter is useful when computing a hash code - for example, in Noda Time the project is built with checked arithmetic for virtual everything apart from hash code generation. When computing a hash code, it's entirely normal for overflow to occur, and that's fine because we don't really care about the result as a number - we just want it as a bit pattern, really.

That's just a particularly common example, but there may well be other times where you're really happy for MaxValue + 1 to be MinValue.