Pure Function

A function with no exec pins — returns values based only on inputs, never mutates state. Re-evaluated on every connected use.

Blueprint function vs custom event vs macro: when to use each

BLUEPRINT FUNCTION: - Has its own execution context, can have inputs/outputs/return value. - Cannot have Delay, Timeline, or latent nodes inside. - Best for: pure logic, calculations, data transformation. - Can be overridden in child BPs (if not pure). CUSTOM EVENT: - Lives in event graph, can be called like a function. - CAN have Delay, Timeline, latent nodes. - Can be Replicated (Server/Client/Multicast). - No return value. Best for: triggered behavior, RPC calls. MACRO: - Inlined at call site — like a code template. - CAN have multiple exec inputs AND outputs. - CAN contain latent nodes. - Best for: reusable flow patterns (e.g. 'IsValidAndCast' check-and-cast pattern). PURE FUNCTION: checked 'Pure' — no exec pins, evaluated on demand. Best for getters.

Macro

An inline-expanded subgraph. Like a function but each use creates a fresh copy at compile time (faster, but more bytecode).

Less (float) — A < B

Delegate

A type-safe function pointer used by Event Dispatchers and bindings. Bind, broadcast, unbind.

BooleanAND — logical AND

OR=BooleanOR, NOT=Not_PreBool, XOR=BooleanXOR

Function

A named, reusable subgraph with inputs + outputs. Cleaner than copy-pasting node clusters.

EqualEqual_FloatFloat — float equality comparison

Calling a function that doesn't exist on the target object

Why: You're calling '{fn}' on an object that doesn't have that function. The function may have been deleted, renamed, or moved to a different class. UE5 can't bind the call at compile time. Fix: Check the target pin's type. Search the Content Browser for the actual class name + look for '{fn}' in its functions. If found, drag a fresh reference and use the proper context menu Call Function path. If gone, find a replacement function or use an Interface call.

Gate — pass or block execution based on open/closed state