Blueprint Function Keywords

Unreal provides a list of function specifiers you can use to expose native code to blueprints. These specifiers allow for different levels of interaction between C++ and Blueprint.

Function Specifiers

• BlueprintCallable: Marks a function as callable from within Blueprint.
• BlueprintPure: Indicates that the function does not modify the state of the object.
• BlueprintNativeEvent: Allows providing a default implementation in C++ with optional Blueprint override.
• BlueprintImplementableEvent: Declares a function in C++ but requires implementation in Blueprint.

All function specifiers are inserted within the UFUNCTION(...) macro above a function declaration.

UFUNCTION(BlueprintCallable, Category="Defaults")
TArray<FName> GetMaterialParameterNames() const;

Multiple function specifiers can be used for additional behavior, though not all are compatible with one another.

// alllowed - a function can both  be callable and pure
UFUNCTION(BlueprintCallable, BlueprintPure, Category="Defaults")
TArray<FName> GetMaterialParameterNames() const;

// error - A function cannot be both a BlueprintNativeEvent and BlueprintImplementableEvent
UFUNCTION(BlueprintCallable, BlueprintNativeEvent, BlueprintImplementableEvent, Category="Defaults")
TArray<FName> GetMaterialParameterNames() const;

BlueprintCallable specifier

This specifier marks a function as callable from within Blueprint. Use BLueprintCallable when you want to allow Blueprints to execute a C++ function.

UFUNCTION(BlueprintCallable, ...)
TArray<FName> GetMaterialParameterNames() const;

BlueprintPure specifier

This specifier indicates that the function does not modify the state of the object (hence the name "Pure") -- it only returns a value based on its inputs.

UFUNCTION(BlueprintCallable, BlueprintPure, ...)
TArray<FName> GetMaterialParameterNames() const;

BlueprintNativeEvent specifier

This specifier allows you to provide a default implementation of a function in C++, which you can then optionally override in Blueprints.

// cleanable.h
UFUNCTION(BlueprintCallable, BlueprintNativeEvent)
bool CanBeCleaned();

// cleanabale.cpp
bool UCleanable::CanBeCleaned_Implementation()
{
    const FGameplayTagContainer PlayerTags = ULittleTrekkerGameInstanceState::Get(this)->GetGameplayTags();
    if (PlayerTags.HasAll(RequiredTagsToClean))
    {
        return true;
    }
    return false;
}

BlueprintImplementableEvent specifier

This specifier allows you to declare a function and define its signature in C++, but require that it be implemented in Blueprint.

Since Unreal knows the function implementation will be handled in Blueprint, there is no need to generate a function definition in the .cpp file.

We use BlueprintImplementableEvent in scenarios where the implementation details are expected to vary significantly across different blueprints.

// worldwidget.h
UFUNCTION(BlueprintImplementableEvent, BlueprintCallable, Category="WorldWidget")
void OnActorChange(AActor* Actor);