WTF Is? A Pure Function

What is a Pure Function in Unreal Engine 4 Blueprints?

[NeonFraction]

I spent so long studying tutorials and the API trying to figure this out and got no where. Thank you so SO much for doing these tutorials. You have no idea how much you're helping. :)

[KvaGram]

Finally a decent explanation.
So a pure function is called EVERY time a node it connects to is called.

[arielquinteros]

Your videos are incredible, I was fighting with how to best organize the pipes of a function that i was constantly needing in different graphs and 68 seconds into your video I was done with this, thank you so much!!!

[ReOp]

How come the 'Find' node for Blueprint Maps is pure when it has two outputs? If I wanna check if something was successfully found, and then use the value found, that's two find calls! Seems so inefficient to calculate the find twice.

[unrealdevop]

Great video, please turn the treble down on your mic though. Sometimes it feels like someone is stabbing me in the ear with a knife.

[stephenmontague]

Great explanation - just a note- the Pure function should not have been marked as Pure, and this rule isn't enforced, but it's considered a bug to do as shown.

From the docs - "Pure Functions promise not to modify state or the members of the class in any way."

So changing the Input Variable as shown shouldn't be done in a Pure function, but beware, since it could be done.

Edit: Although there's a difference between Pure Const and just Pure - so if the variable modified was not a Class member, that is, just a local variable, then it may have been technically Pure, but I would still avoid doing this.

[naghekyan]

If I understood correctly, you say pure functions does not have any inputs, right?