Description
Constructs the optional's value in-place from the given arguments, destroying any previously held value first. Returns a reference to the newly constructed value.
Caveats & Gotchas
- • If the constructor called via Emplace leaves the object in an 'unset' intrusive state (i.e. equal to FIntrusiveUnsetOptionalState), a checkf fires in non-shipping builds. Intrusive optional types must not emplace their own unset sentinel.
- • Emplace always destroys the existing value before constructing the new one, even if the type supports assignment. This is intentional to support non-assignable types but means the destructor always runs on replacement.
- • The returned reference is valid only until the next mutation of the TOptional (Reset, Emplace, or assignment). Do not store it persistently.
Signature
template <typename... ArgsType>
OptionalType& Emplace(ArgsType&&... Args)Parameters
| Name | Type | Description | Default |
|---|---|---|---|
| Args | ArgsType&&... | Arguments forwarded directly to OptionalType's constructor. | — |
Return Type
OptionalType& Example
In-place construction of a complex value C++
TOptional<FTransform> CachedTransform;
// Construct FTransform directly inside the optional, no temporary:
CachedTransform.Emplace(FRotator(0, 90, 0), FVector(100, 0, 0));
if (CachedTransform.IsSet())
{
FVector Loc = CachedTransform->GetLocation();
}See Also
Tags
Version History
Introduced in: unknown
| Version | Status | Notes |
|---|---|---|
| 5.6 | stable | — |
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