Zstandard compression support in .NET libraries in .NEt 11 means significantly faster compression and decompression compared to existing algorithms while maintaining competitive compression ratios. New APIs include a full set of streaming, one-shot, and dictionary-based compression and decompression capabilities. Also featured is a per-year cache for time zone transitions, improving performance for time conversions. The cache stores all transitions for a given year in UTC format, eliminating repeated rule lookups during conversions.
C# 15 in .NET 11 Preview 1 introduces collection expressions arguments, a feature that supports scenarios where a collection expression does not produce the desired collection type. Collection expression arguments enable developers to specify capacity, comparers, or other constructor parameters directly within the collection expression syntax. C# 15 also brings extended layout support, by which the C# compiler emits the TypeAttributes.ExtendedLayout for types that have the System.Runtime.InteropServices.ExtendedLayoutAttribute applied. This feature is primarily intended for the .NET runtime team to use for types in interop scenarios.
With F# 11 in .NET 11 Preview 1, the F# compiler has parallel compilation enabled by default and features faster compilation of computation expression-heavy code. ML compatibility has been removed, though. The keywords asr, land, lor, lsl, lsr, and lxor — previously reserved for ML compatibility — are now available as identifiers. Microsoft said that F# began its life as an OCaml dialect running on .NET, and for more than two decades, the compiler carried compatibility constructs from that heritage including .ml and .mli source file extensions, the #light "off" directive for switching to whitespace-insensitive syntax, and flags like --mlcompatibility. These served the language well during its early years, providing a bridge for developers coming from the ML family, the company said, but that chapter comes to a close. About 7,000 lines of legacy code have been removed across the compiler, parser, and test suite.
