Mojo nightly

Mojo nightly introduces compiler optimizations that speed up compilation of files with large collection literals by about 1.3x, renames the @parameter decorator to @__parameter, and adds namespace semantics for directories. The update also makes StringDict Writable, adds experimental 6-bit float types from the Open Compute microscaling specification, and renames UnsafeMaybeUninit to MaybeUninit with safer conformance gating.

Mojo nightly This version is still a work in progress. Highlights - Code that performs many implicit conversions, most visibly large collection literals, compiles faster: the compiler no longer runs parameter inference on constructors that cannot be used for an implicit conversion in the first place. Files that are mostly data, such as the standard library's Unicode lookup tables, compile about 1.3x faster. Language changes - Renamed the @parameter decorator on parametric closures to @ parameter . The deprecated @parameter if / @parameter for forms are unchanged; prefer comptime if / comptime for for compile-time control flow. - The module & package system: - Directories may now have "namespace" semantics; a single directory name may resolve across distinct locations on disk which share that name. . ├── one │ └── foo │ └── bar.mojo └── two └── foo └── baz.mojo Compiles with -Ione -Itwoimport foo.barimport foo.baz - Importing functions with the same name from different modules, combining them into one overload set, is now an error, following a period of deprecation. - Intra-package accesses without explicit import s are now an error, following a period of deprecation. - Library changes - StringDict now conforms to Writable when its value type is Writable , matching the existing behavior of Dict . This lets you print a StringDict or convert it to a String . - The chars argument of strip , lstrip and rstrip on StringSpan , String and StringLiteral is now an ImmStringSpan , so a mutable string is accepted as chars , including the string being stripped s.strip s . - StringDict. getitem now accepts a StringSpan , so you can index a StringDict with a borrowed string view without first allocating a String just to perform the lookup. - Renamed the variadic type-list parameter on Tuple and VariadicPack to Ts , standardizing the naming convention used across the standard library. The old name, element types , remains as a deprecated alias. - Added experimental DType.float6 e2m3fn and DType.float6 e3m2fn , the two 6-bit encodings from the Open Compute microscaling specification https://www.opencompute.org/documents/ocp-microscaling-formats-mx-v1-0-spec-final-pdf . Both are finite-only, so neither has an inf nor a NaN encoding.These are experimental storage formats for packed weights rather than general-purpose numeric types, and standard library support is deliberately partial. As with the existing DType.float4 e2m1fn , they are excluded from is numeric , arithmetic is not implemented, and converting to or from another floating-point type is unsupported on every target, so values cannot be printed either. - Array now conforms to Defaultable when its type T is also Defaultable . - Deprecated is trivially movable , is trivially copyable , and is trivially deletable in std.memory in favor of IsTriviallyMovable T , IsTriviallyCopyable T , and IsTriviallyDeinitable T in std.traits . The replacements are comptime predicates rather than functions, so drop the call parens at use sites, for example IsTriviallyCopyable T instead of is trivially copyable T . - Renamed UnsafeMaybeUninit to MaybeUninit . It conforms to Movable , Copyable / ImplicitlyCopyable , and Deinitable only when the contained type's own move, copy, or implicit deinitializer is trivial, since moving, copying, or destroying a MaybeUninit only touches its raw bits, never the contained value's own lifecycle methods. Gating conformance this way turns what would otherwise be silent memory-safety bugs into compile-time errors. - Atomic is now parameterized on a value type T instead of a DType . Update call sites from Atomic DType.float32 to Atomic Float32 . The atomic operations load , store , fetch add , compare exchange , and so on still only support Scalar types. - Added Pointer T .unsafe write def - T , which initializes the pointee with the value returned by a closure, constructing it directly in place rather than moving an already-constructed value there. Unlike unsafe write var T , this does not require the pointee type to be Movable . - Pointer.mut cast is now deprecated. Developers should prefer using explicit mutabilites at the callsite via MutPointer or ImmPointer . If mut casting is needed it should try to be avoided - you can use unsafe mut cast . - The following APIs have been migrated to unified closures: sort , debug assert , Span.apply . - Uncaught exceptions now print to stderr , not stdout . Tooling changes mojo doc now reports the condition of a conditional trait conformance, and the generated API docs show it alongside the trait. Previously the condition was dropped, making a conditional conformance indistinguishable from an unconditional one. Also fixed rendering of some where clauses. Removed This release completes the removal of APIs deprecated during the v1.0 cycle. - Removed the temporary InlineArray alias for Array , including its re-exports from std.collections and the prelude. Use Array directly. - Removed the std.gpu.profiler module and its ProfileBlock context manager. It timed host wall-clock, not GPU work, and reported the elapsed time with the operands reversed. Time a block of host code withdirectly, and use a GPU profiler such as Nsight Systems or perf counter ns rocprof for device timings. - Removed memcmp and its std.memory re-export. Use unsafe memcmp instead. - Removed the validate parameter from, which now always validates. Passing b64decode validate=False did not skip any work on valid input; it only turned characters outside the base64 alphabet into silently corrupt output bytes. Drop validate=True from existing calls; calls that relied on the default now raise instead of returning garbage. - Removed the origin aliases left over from the Immut to Imm and External to Untracked renames. Use the surviving spelling in each case: ImmOrigin for ImmutOrigin , ImmUnsafeAnyOrigin for ImmutUnsafeAnyOrigin , ImmStaticOrigin for StaticConstantOrigin , UntrackedOrigin for ExternalOrigin , MutUntrackedOrigin for MutExternalOrigin , and ImmUntrackedOrigin for both ImmutUntrackedOrigin and ImmutExternalOrigin . - Removed the pre-unification pointer aliases MutUnsafePointer , ImmUnsafePointer , ImmutUnsafePointer , ImmutOpaquePointer , ImmutPointer , and OptionalUnsafePointer . Use MutPointer , ImmPointer , ImmOpaquePointer , and OptionalPointer instead. UnsafePointer itself remains available, but is deprecated in favor of Pointer . - Removed the raw memory functions superseded by their unsafe -prefixed spellings: memcpy , memset , memset zero , uninit move n , uninit copy n , and destroy n . Use unsafe memcpy , unsafe memset , unsafe memset zero , unsafe uninit move n , unsafe uninit copy n , and unsafe destroy n instead. - Removed the size aliases left from the size to length rename: SIMD.size , Array.size , TypeList.size , and the SIMDSize alias for SIMDLength . Use length and SIMDLength . - Removed the as immutable and get immutable methods on Pointer , Span , and StringSpan . Use as imm . - Removed the ImmutSpan alias. Use ImmSpan . - Removed String.as string slice . Construct a StringSpan from the string instead: StringSpan my string . - Removed the ImplicitlyDestructible and ImplicitlyDeletable aliases. Use Deinitable . - Removed the deprecated ownership-transfer methods: List.steal data and OwnedPointer.steal data are now unsafe take allocation , OwnedPointer.take is into inner , and Variant.take and Variant.unsafe take are unwrap and unsafe unwrap . - Removed the Pointer methods superseded by their unsafe -prefixed spellings: as noalias ptr , destroy pointee , destroy pointee with , init pointee move , init pointee copy , and init pointee move from . Use unsafe as noalias , unsafe deinit pointee , unsafe deinit pointee with , unsafe write , and unsafe write move from . The Pointer.type alias for Pointer.T is gone as well. - Removed the ConditionalType type function and the std.utils.type functions module. Use the ternary expression T if cond else U . - Removed trait downcast . Constrain on the trait instead, with conforms to type of src , Trait in a where clause or a comptime assert . - Removed the parametric benchmark.run func overloads. Pass the function as an argument to run f instead, which accepts a unified closure. - Removed AnyCoroutine , Coroutine and RaisingCoroutine from the prelude, and made the module that defines them private. Mojo's async support is unfinished, and these types being globally visible led people to build on an API that carries no stability guarantees. async def is unaffected: the compiler still synthesizes these types for you, so they continue to appear in inferred types and diagnostics. There is no supported way to name them directly. - Removed the async task API from the public std.runtime.asyncrt module, which is now private. initialize runtime and parallelism level are unaffected and have moved up to the std.runtime package, so import them from std.runtime instead of std.runtime.asyncrt . - Removed support for .mojopkg files after a period of deprecation. Use .mojoc files instead. Fixed - mojo build --emit asm and --emit llvm now always write the offload kernel files next to the host output file. Building a kernel that an earlier build had already compiled could write them into the earlier build's output directory, or skip them with no diagnostic. - Parametric raises now accepts any primary expression as the thrown type in a function signature, matching the syntax positions where types otherwise appear. This most notably fixes raises Self.SomeAssocType on trait and struct methods, which would previously fail with an error. The parenthesized workaround raises Self.DriveErrorType is no longer required. - An integer range with a step of zero is now always empty. It previously used to be an infinite loop - iterating forever at runtime, and hanging the compiler at comptime. - Fixed ceildiv returning 0 for unsigned operands near the type's maximum value. The unsigned code path computed numerator + denominator - 1 , which overflows and wraps for large operands; it now derives the ceiling from the floor division and remainder instead. - Counter.most common n now returns all elements when n exceeds the number of unique elements, matching Python, instead of aborting. - os.path.join now inserts separators based on the accumulated path rather than the first argument, so join "/", "a", "b" returns /a/b previously /ab and join "a", "b/", "c" returns a/b/c previously a/b//c . - base64.b64decode now raises an error when the input length is not divisible by 4 instead of reading past the end of the input or aborting when asserts are enabled . - On macOS, os.stat and os.lstat no longer return a negative st mode for regular files. The underlying mode t and nlink t C type aliases were declared as signed 16-bit integers, but macOS defines them as unsigned, so any mode with the S IFREG bit set every regular file sign-extended into a negative Int . - PythonObject no longer leaks a CPython reference per positional argument when calling a Python object, nor when setting an item, attribute, or set literal element.