How closely related are Blueprints and C++?

There is a video on youtube that a programmer creates lazer eyes with blueprint and he says he is great at blueprint because its just another way of coding: Unreal Engine 4 - Firing mah lazors - Done entirely in blueprint (Part 1 of 2) - YouTube , So can you use most of the C++ language in blueprints?, or are there certain limitations to blueprints?

That video is an hour and 40 minutes long. It’s probably better you email the author and ask them to clarify what they meant by that statement instead of asking what they meant here.

Blueprints and C++ are linked. If you can’t do something in Blueprints you can just make a C++ function to handle it. This can be done to a Bluepint after it was created, by making a new C++ Blueprint class and then re-basing the BP to it.

Most gameplay code can be done in Blueprints.

well it doesn’t really matter if you are using blueprint or c++…
blueprint is just another workflow for creating code… it takes all your blueprint stuff and compiles to machine code…
in that way it doesn’t matter if it first was a c++ class or if it was blueprint.

if you are creating a new c++ class you decide what of your calls will be visible to blueprint…
so c++ is definitely mightier than blueprint…
But for game development however i consider it just as mighty as c++ and here is why:

everything you come in touch with in order to create your project the guys at epic already exposed to blueprint.
if not (i for example have to write my own network manager) you have to use c++ and then you can expose it’s functionallity to blueprint

also interessting: it is not possible to look into blueprint after you compiled it…
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