Xo 0.24 release notes

Introduction

Xo 0.24 makes native Maps and Sets a hybrid persistent map, which takes a mixed CRUD server at 1024 connections from 18.0k to 83.0k requests per second. Native code generation is level with LLVM on arm64 and about 6 percent behind on amd64, builds are faster, and the standard library gains XML, big numbers, compression, and a streaming JSON decoder.

Changes to the language

• Moves of the move-only builders are flow sensitive: a return, break, continue, or failing ? ends its path’s moves, so a value moved there is still usable after the branch (decision 0300).
• embed puts files in the binary (decision 0304).
• A program’s own values convert to the capability interfaces (Fs, Proc, Env, Net) on the native backends (decision 0307).
• Wire names per format for JSON, SQL, and XML, and derive Xml (decision 0315).
• Prelude additions.

Compiler and runtime

• Native Maps and Sets are the hybrid persistent map by default; the micro benchmarks stay within 1.2 times the lists (decision 0291).
• Preemption polls on amd64 and on LLVM’s x86-64 code, with the thread-local table no longer reused across a poll (decision 0286).
• Native code generation level with LLVM on arm64 and about 6 percent behind on amd64 (the comparison).
• Faster builds: std interface hashing from tokens, per-file LLVM test splits, a run cache for std module tests, and reference counting insertion in about half its cold time.
• The Go backend compiles path and uuid from their Xo source and supports tuples of up to 64 elements (decision 0312).

Standard library

• std/xml (decision 0314).
• std/big, with Karatsuba multiplication and recursive division (decision 0311).
• JSON omitempty and a streaming decoder (decision 0309).
• std/compress and gzip responses; client_ip.
• The HTTP/1.1 client keeps connections alive (decision 0303).

Tools

• xo def, refs, rename, and symbols cover runtime names, fields, variants, and interface methods.
• The strict inliner verifier runs in xo dev goldens and codegen checks.
• Every Go test names the xo it runs and refuses a stale one.
• --no-preempt; xo build --profile.
• Backend cache pruning fixed (an overflow, concurrent accounting, a prune version guard).

Fixes

• CI and fresh builds work again: 0.23.0 cannot build them, because its inliner verifier rejects main.