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[Stdlib] Add by-index field_at[idx] to reflection#6694
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BEGIN_PUBLIC [Stdlib] Add by-index `field_type_at[idx]` to reflection Add `reflect[T].field_type_at[idx]`, the by-index dual of the existing by-name `reflect[T].field_type[name]`. It returns `Reflected[FieldT]` for the field at `idx`, reusing the same per-index concrete-type plumbing that `field_ref[idx]` already relies on. Unlike the by-name form, the index form composes where only the field index is available, such as inside a `comptime for` over a struct's fields in generic code, and `T` may be a generic type parameter. This lets a reflection-derived serializer recover each field's concrete type by index and peel a wrapper such as `Optional[T]` once, instead of enumerating the inner type by hand. A separate name (rather than an overload of `field_type`) is required because `comptime` member aliases cannot be overloaded on parameter type. Resolves modular#6645. END_PUBLIC Assisted-by: AI Signed-off-by: Manuel Saelices <msaelices@gmail.com>
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BEGIN_PUBLIC [Stdlib] Trim docstrings and comments for field_type_at Condense the `field_type_at` docstring, the implementation comment, and the new test docstrings. END_PUBLIC Assisted-by: AI Signed-off-by: Manuel Saelices <msaelices@gmail.com>
BEGIN_PUBLIC [Stdlib] Add changelog entry for field_type_at Document the new by-index `reflect[T].field_type_at[idx]` reflection accessor under Library changes. END_PUBLIC Assisted-by: AI Signed-off-by: Manuel Saelices <msaelices@gmail.com>
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Pull request overview
Adds a new by-index reflection accessor to std.reflection so generic code iterating over struct fields by index can recover each field’s concrete type as a Reflected[FieldT] handle (mirroring the existing by-name field_type[name]).
Changes:
- Added
reflect[T].field_type_at[idx]as acomptimemember alias returningReflected[FieldT]for the field at indexidx. - Added new stdlib reflection tests covering by-index lookup, parity with by-name lookup, composability, generic usage, and wrapper peeling.
- Documented the new API in the nightly changelog.
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Good catch, thanks. Fixed in 4e483be: the "Member shape" note now lists both field_type[name] and field_type_at[idx] as the type-returning members.
BEGIN_PUBLIC [Stdlib] Update reflection member-shape note for field_type_at The "Member shape" note in `Reflected` said `field_type[name]` was the only type-returning member; update it to also list `field_type_at[idx]`. END_PUBLIC Assisted-by: AI Signed-off-by: Manuel Saelices <msaelices@gmail.com>
…ield-type-at # Conflicts: # mojo/docs/nightly-changelog.md # mojo/stdlib/std/reflection/reflect.mojo
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field_type_at[idx] to reflectionfield_at[idx] to reflection
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Summary
Adds
reflect[T].field_at[idx], the by-index dual of the existing by-namereflect[T].field[name]. It returnsReflected[FieldT]for the field at indexidx, reusing the per-index plumbingfield_ref[idx]already relies on.Resolves #6645.
Why
Unlike the by-name form (concrete
T, name as aStringLiteral), the index form works where only the field index is available, such as inside acomptime forover a struct's fields in generic code. This lets a reflection-derived serializer recover each field's concrete type by index and peel a wrapper likeOptional[T]once, instead of enumerating the inner type by hand.Naming
A separate name (not an overload of
field) is required becausecomptimemember aliases cannot be overloaded on parameter type: the compiler rejects two same-named aliases withinvalid redefinition.field_atmatches the index-keyed siblingsfield_ref[idx]andfield_offset[index=...].Tests
7 new tests in
test_reflect.mojo, all passing (39/39): by-index lookup, parity with the by-name form, composable handle, type annotation, first index, field-type recovery through a generic[T: AnyType]parameter, and peeling anOptional[T]inner type.A changelog entry is added under Library changes.
Assisted-by: AI