Start with the idea
There is no implicit numeric promotion: adding a u8 to a u32 is a compile error until you convert. In a debug build an overflowing add panics rather than silently wrapping, and in release it wraps — which is why the standard library gives you checked_, wrapping_, and saturating_ variants to say which one you meant.
The example shows why an overflow policy must be explicit. A u8 can hold values from 0 through 255, so 250 + 10 does not fit. checked_add returns None rather than a number; wrapping_add cycles around to 4; saturating_add clamps at 255. These are three different product decisions. A count of completed tasks probably should not wrap from 255 to 4, while a circular sequence number may intentionally do so. Pick the behavior from the domain before choosing the method.
The later as cast illustrates another boundary. Converting 300_i32 to u8 with as keeps only the low eight bits, yielding 44.
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