The assert() method's behavior is different between 3.x and 4.0 .

[Daylily-Zeleen]

In 4.0, assert() is second argument message must be a static String, but in 3.x, it can be dynamic.

For example:

var list: Array = []

func get_value(idx: int):
    # Valid in 3.x, invalid in 4.0
    assert(idx < list.size() and idx > 0, "Invalid index: %d"%idx)
    return list[idx]

Of course, we can use other way to express the detail error message for the assert(), like code a comment near the assert(),
but obviously, implement dynamic String for message is the best way.

What is the reson why 4.0 let message static?

[Zireael07]

is a bug: godotengine/godot#47157

[Daylily-Zeleen]

But it is written in help document.

[Calinou]

But it is written in help document.

A documented bug can still be a bug 🙂

I think someone documented this behavior thinking it was intentional, but it remains a bug nonetheless.

[Daylily-Zeleen]

I see. Thanks for your reply.