Course of Raku / Advanced / More about built-in types / Native types 🆕

Sized types and overflow

Besides the plain int, Raku has integers of a fixed bit width: int8, int16, int32, int64, and their unsigned partners uint8, uint16, uint32, uint64. The number is how many bits the value occupies.

A fixed width means a fixed range. An int8 holds values from -128 to 127; a uint8 holds 0 to 255. Because the storage cannot grow, going past the top wraps around to the bottom — this is overflow:

my int8 $i = 127;
$i++;
say $i; # -128

Adding one to the largest int8 does not produce 128 (which would not fit); it wraps to the smallest value, -128. Unsigned types wrap too:

my uint8 $u = 255;
$u++;
say $u; # 0

This is the opposite of a normal Int, which simply grows as large as needed and never overflows. The trade-off is the whole point of sized natives: you accept a fixed range in return for predictable, compact, fast storage.

Use a sized native type when you know the range of your data and want the efficiency — for example, bytes of binary data in a uint8 array. For ordinary arithmetic where numbers may grow without bound, stick with Int.

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