REPOSITORY CODING · MEDIUM
Require every writer union branch to be readable
A writer union containing int and string is not wholly compatible with a long reader, even though its observed int branch can migrate. Separate schema coverage from observed-value resolution.
Typed schema evolutionSchema resolution laboratory
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Task requirements and environments
PHP · 55 minute session
- Resolve a bounded writer/reader schema pair and up to 20 JSON records. Primitive types are null, boolean, int (signed 32-bit), long (safe JSON integer), double, string and lowercase hex bytes. Records, arrays, maps, enums, fixed bytes and tagged unions are supported to depth eight; field/symbol/branch counts have explicit limits. Named types are inline declarations, not unresolved external references.
- Compatibility means every writer value can be read. Numeric widening is int->long/double and long->double, never narrowing. Every writer union branch needs a reader match; a reader union picks its first compatible branch. Union values are {branch:tag,value}, where named branches use their name.
- Record names may match reader aliases. Reader fields match writer names first, otherwise one unambiguous reader field alias. Drop writer-only fields. Missing reader fields require a validated default, including explicit null. For union defaults, the raw default must match the first branch and migration wraps it in that branch tag. Unknown writer record fields and malformed record values are errors.
- Arrays/maps resolve recursively and preserve map key spelling. Enum writer symbols must exist in the reader or use a declared reader default that belongs to its symbols. Fixed types require matching names/aliases and byte sizes. Validate all schema defaults before migrating any record.
- Return compatible for the complete schema space and independent per-record migration results, allowing an observed union branch to migrate even when other writer branches are incompatible. Schema errors fail the request; value errors identify their field/index path. PHP and Symfony share the native resolution modules and public preview.
Symfony · 55 minute session
- Resolve a bounded writer/reader schema pair and up to 20 JSON records. Primitive types are null, boolean, int (signed 32-bit), long (safe JSON integer), double, string and lowercase hex bytes. Records, arrays, maps, enums, fixed bytes and tagged unions are supported to depth eight; field/symbol/branch counts have explicit limits. Named types are inline declarations, not unresolved external references.
- Compatibility means every writer value can be read. Numeric widening is int->long/double and long->double, never narrowing. Every writer union branch needs a reader match; a reader union picks its first compatible branch. Union values are {branch:tag,value}, where named branches use their name.