fix(binder): bind nullable value-type properties over underlying type#161
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A nullable value-type DTO property (int?, bool?) inferred TArgument as Nullable<T>, so a value-object factory over the underlying type (int -> Outcome<T>) could not bind as a method group (CS0411). Add a struct-constrained SimpleProperty/ListOfSimpleProperties overload whose selector carries Nullable<TArgument>: structurally more specific than the reference overload, it wins for value-type properties and surfaces the underlying non-nullable type, while reference and string properties keep resolving to the original overload. Lists of value types get a dedicated converter that unwraps each present element and records a null element as a missing argument under its indexed path. Refs: #144
Record the public-API-contract decision behind the value-type selector overloads: a nullable value-type DTO property binds through a dedicated struct-constrained overload whose selector carries Nullable<TArgument> and whose converter runs over the underlying non-nullable type. Drafted as Proposed and indexed; the maintainer decides its status. Refs: #144
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Summary
A nullable value-type DTO property (
int?,bool?) could not bind through a method-group converter over its underlying type — the call failed to compile withCS0411, becauseSimpleProperty(r => r.Prop)inferredTArgument = Nullable<int>and the converter stage then expectedFunc<Nullable<int>, Outcome<T>>. This adds struct-constrained selector overloads so such properties bind directly against anint-taking converter, and records the API-shape decision as ADR-0008 (Proposed).Type of change
Changes
where TArgument : structoverloads ofSimplePropertyandListOfSimpleProperties. Under the constraint,TArgument?is the constructedNullable<TArgument>— structurally more specific than the reference overload's bareTArgument— so the value-type overload wins for a nullable-value-type property and surfaces the underlying non-nullable type, with noCS0111/CS0121. Reference and string properties keep resolving to the original overloads.ListOfSimpleValuePropertiesConverter<TRequest, TArgument>: the value-type counterpart of the list converter — it unwraps each present element and records anullelement as a missing argument (REQUEST_ARGUMENT_REQUIRED) under its indexed path.AsOptionalValue, fallback,bool?, lists (required / null-element / invalid-element / optional-absent),string?andList<string?>regressions, and the non-nullableintguard.doc/RequestBinder.en.mdanddoc/RequestBinder.fr.md(lockstep).Proposed) recording the struct-constrained-overload decision, and index it.Testing
dotnet build FirstClassErrors.sln— succeeded, 0 warnings / 0 errors.dotnet test FirstClassErrors.sln— all green (Cli 63, Core 423, Analyzers 85, GenDoc 136, PropertyTests 21, RequestBinder 75), 0 failed.FirstClassErrors.Analyzers.UnitTests) — 85 passed (run as part of the full-solution suite above).The binder suite is 75 tests = 62 existing + 13 new; no regression.
Documentation
doc/updated — RequestBinder guide (EN).doc/RequestBinder.fr.mdwas updated in lockstep with the English guide;doc/README.fr.mditself needed no change.Architecture decisions
Proposed: ADR-0008ADR-0008 records the public-API-contract decision (the struct-constrained overload shape) surfaced by #144 as
architecture+blocking, gated on the v1 API freeze. Drafted asProposed; the maintainer decides its status.Related issues
Closes #144
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