Why is rune an alias for int32 in Go, and not uint32?

Despite its primary purpose of representing character values, the rune type in Go is not defined as an alias for uint32. Instead, it is an alias for int32. This choice may seem counterintuitive given that characters are typically represented by positive values.

The rationale behind this decision is rooted in the role of rune as a placeholder for Unicode codepoints, which extend beyond the range of ASCII characters. Unicode codepoints can be either positive or negative, and using int32 allows Go programmers to detect potential overflows or errors during arithmetic operations involving runes.

Uint32, on the other hand, is an unsigned integer type that can only hold positive values. This would prevent the detection of negative rune values, which could lead to subtle errors in code that relies on identifying overflow situations.

In contrast, the byte type, an alias for uint8, is used specifically for representing ASCII characters. As ASCII characters are always positive, using an unsigned integer type for byte is appropriate.