Why does Array Find return -1 for a struct that exists?

BP Array Find uses operator== which Blueprint structs don't define automatically. Override == in C++ for the struct, or use a ForEachLoop with manual field comparison.

How do I override == on a struct?

In C++: bool operator==(const FMyStruct& A, const FMyStruct& B) { return A.Id == B.Id; }. Define inline in the header. BP can now Find correctly.

What's Find by Predicate?

BP doesn't have it natively, but you can ForEachLoop and compare on a key field manually. Returns first match index. More verbose but works for any comparison logic.

Fix: Unreal BP Array Find Returns -1 with Struct

Quick answer: Define operator== on the C++ struct. BP Array Find then works. Without ==, BP’s Find can’t compare struct values element-wise.

BP Array Find searches an FInventoryItem struct array for a matching item. Returns -1 even when the item is present. Struct equality is not defined.

The Symptom

Array Find with a struct argument always returns -1 except for very simple structs (single int field, sometimes).

The Fix

USTRUCT(BlueprintType)
struct FInventoryItem
{
    GENERATED_BODY()
    UPROPERTY(EditAnywhere, BlueprintReadWrite) int32 Id;
    UPROPERTY(EditAnywhere, BlueprintReadWrite) int32 Count;

    bool operator==(const FInventoryItem& Other) const
    {
        return Id == Other.Id;   // match by Id only
    }
};

Now BP Array Find compares by Id; matching elements are found.

BP-Only Workaround

Use ForEachLoop and break on a manual field comparison:

ForEachLoop(InventoryArray):
  Element.Id == TargetId -> SET FoundIndex = ArrayIndex; Break

Verbose but works without C++ changes.

Verifying

Find an item that exists. Returns its index. Without ==: -1.

“Define equality. Find works.”

Related Issues

For Blueprint Interface cooked, see interface cast. For Blueprint async pending, see async task.

Equality defined. Searches work.