Bounded Strings

Text on a small machine needs a firm storage bound. A string[N] owns room for at most N content bytes and keeps a current logical length alongside them. The current language admits capacities from 1 through 253.

var source as string[6] = "A\0B"
var copy as string[6]

The embedded zero is ordinary content. source.length is 3, not 1. Nucleus string operations use the stored length and do not stop at the first zero.

Reading and replacing bytes

source[index] produces a u8 byte path. The index must be less than the current length, not merely less than the capacity. Assignment replaces one existing byte:

copy[2] = 'C'

It does not append, change .length or expose unused capacity. A concrete string[N] may read .length, but it cannot assign that property. Chapter 9 introduces the open string view used by library routines that construct text.

Whole-string assignment

Two bounded strings may be assigned only when their concrete types are identical. copy = source copies the complete fixed object, including its logical length and its sealed padding. It is not a character-by-character conversion and does not accept a different capacity.

The runtime representation keeps the payload zero-filled and a zero byte after the capacity. This guarantees that a terminator-reading machine routine cannot run beyond the object. It does not promise a C string of logical length L: an embedded zero can make such a routine stop early. Source-level Nucleus operations remain governed by .length.

The companion copies "A\0B", changes its final byte to C, and proves that the logical length remains three. It leaves observed equal to 432.

var source as string[6] = "A\0B"
var copy as string[6]
var observed as u16 = 0

sub main()
    copy = source
    copy[2] = 'C'
    observed = u16(copy.length) * 100 + u16(copy[0]) + u16(copy[2])
end

Summary

• string[N] has fixed capacity and a separate current length.
• Embedded zero bytes are ordinary content.
• Indexing is checked against the current length.
• Byte assignment does not append or change the length.
• Whole-object assignment requires the same concrete capacity.

See bounded-string types and the runtime representation. The checked companion is 07-strings.nu.