Fable 5.0.0-rc.4 released!

NewsBot · 19 March 2026 19:19

Fable 5.0.0-rc.4 has been released.

Fixed

[JS/TS] Fix Array.zeroCreate producing null for user-defined struct (value type) elements instead of a default-initialized instance (by @MangelMaxime)

[All] Fix interpolated string holes missing format specifiers in State.fs and Python/Replacements.fs (code scanning alerts 1144, 1145, 1512)

[Rust] Replace unsafe .IsSome && .Value option pattern with Option.exists in Fable2Rust.fs (code scanning alert 1125)

[JS/TS] Fix Unchecked.defaultof<char> being emitted as null instead of '\0' (by @MangelMaxime)

[JS/TS] Fix static val mutable fields declared with [<DefaultValue>] not being zero-initialized (fix #2739) (by @MangelMaxime)

[JS/TS/Python] Fix record/struct types augmented with static let or static member val generating extra constructor parameters for each static field, causing constructor arguments to be assigned to wrong slots (by @MangelMaxime)

[TS] Annotate System.Collections.Generic.IList<T> as MutableArray<T> (by @MangelMaxime)

[JS/TS] Fix ResizeArray index getter/setter not throwing IndexOutOfRangeException when index is out of bounds (fix #3812) (by @MangelMaxime)

[Beam] Fix unused term warning in try/catch when exception variable is not referenced (by @dbrattli)

[Beam] Fix “no effect” warning for pure BIF calls (self/0, node/0) in non-final block positions (by @dbrattli)

[Beam] Fix reraise() generating unbound MatchValue variable — use raw Erlang reason variable for re-throw (by @dbrattli)

[Beam] Fix Erlang.receive<'T>() resolving to timeout overload due to F# unit argument (by @dbrattli)

[JS/TS] Generate comments for members in class decorated with [<AttachMembers>] (by @MangelMaxime)

[Beam] Fix [<ImportAll>] generating invalid module:*() Erlang code when binding is used as a value (by @dbrattli)

[Beam] Fix string slicing and Substring with compound expressions producing wrong binary:part length due to missing parentheses in emitted Erlang (by @dbrattli)

[Beam] …

Link: Release 5.0.0-rc.4 · fable-compiler/Fable · GitHub