A String keeps short text in place, and a view inside an element dies with the array

Decided by the user on 2026-11-04: “We also can have short string inside the String”, answering the question T-0156 put. Built in r114.

The question. A String was a List<u8> and its closing zero, so every non-empty string allocated. std::string keeps up to 15 bytes inside the object. In tests/bench_programs/words, nearly every word is that short, so the Dazzle half made millions of allocations its C++ half does not. Keeping short text in place changes what a String’s tie means. A view into a short string points into the String itself, so moving the String ends it, and so does moving the list it is an element of: growing, sorting or swapping it. Until then §6.7 said a view into one element’s text survived pushing another. The alternatives were a separate SmallString, or leaving String as it was and relying on regions.

The resolution.

String keeps text of up to 15 bytes in place (§14.2), in two machine words that hold either the text and its zero or where longer text is and how much room it has. It stays 32 bytes: those words, the length, and the allocator.
A view inside an element dies with the array (§6.7). What a path reaches from an element through no pointer’s storage is in the element’s own bytes, which move when the array does: list[i].as_str() for a short string, and a method’s reference into an element, list[i].left_of(). A reference read through the element, &list[i].name, already died this way; a view through a method did not, which was a hole for any type, not only String. What an element owns behind a pointer stays where it is.
A tie naming plain data names those bytes (§6.7). tie @text = m_store, an array of numbers, names the bytes inside the value, so a clause can kill them though they own nothing. Before, a tie on plain data named nothing a clause could compare.

What it changes for a program. A view into a list element’s text, kept across a push, sort, sort_by, swap or reverse of that list, is now DZ0413. Every program in the repository already got its views again after such a change.