Description
Template constraint applied to TSharedPtr's converting constructors and assignment operators. Ensures at compile time that the source pointer type is implicitly convertible to the target type, preventing silent type-unsafe conversions.
Caveats & Gotchas
- • UE_REQUIRES is an Unreal macro that expands to a C++20 requires clause or a std::enable_if fallback depending on the compiler. It is not a callable function — it appears in the template parameter list and produces a hard compile error if not satisfied.
- • For downcasting (base* to derived*) use StaticCastSharedPtr() or ConstCastSharedPtr(). These bypass the UE_REQUIRES constraint via explicit cast constructors that are intentionally not constrained.
- • The constraint applies to the converting constructors from TSharedPtr<OtherType>, TSharedRef<OtherType>, and raw pointer constructors, but not to the StaticCastTag/ConstCastTag constructors used by the cast helpers.
Signature
UE_REQUIRES(std::is_convertible_v<OtherType*, ObjectType*>)Parameters
| Name | Type | Description | Default |
|---|---|---|---|
| OtherType | template parameter | The type of the incoming pointer or shared pointer. The constraint enforces that OtherType* is implicitly convertible to ObjectType*, enabling safe upcasting. | — |
Example
Implicit upcast allowed; downcast requires StaticCastSharedPtr C++
TSharedPtr<FDerived> DerivedPtr = MakeShared<FDerived>();
// OK: FDerived* is convertible to FBase* (upcast)
TSharedPtr<FBase> BasePtr = DerivedPtr;
// ERROR: FBase* is NOT convertible to FDerived* — UE_REQUIRES fails
// TSharedPtr<FDerived> Back = BasePtr;
// Correct downcast:
TSharedPtr<FDerived> Back = StaticCastSharedPtr<FDerived>(BasePtr);See Also
Tags
Version History
Introduced in: 5.0
| Version | Status | Notes |
|---|---|---|
| 5.6 | stable | — |
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