Null Value VS Unknown Value in Framework Types

Terraform Providers Plugin Development
1

I utilize the ValueStringPointer method to access a value in a provider model (similar to this example) in plugin development with the framework. But I am confused about the difference between null value and unknown value.

In the docs, it said ValueStringPointer returns a pointer to the known string value, nil for a null value, or a pointer to "" for an unknown value. But what is considered as a null value and what’s considered as an unknown value? If the user never set that field in the template, would it be null or unknown?

2

My understanding (this is not the voice of authority):

If the attribute has Optional: true and Computed: false, the config and plan value for that attribute will be Null if the user didn’t set it. The attribute is not permitted to sprout a value during the apply phase.

If the attribute has Computed: true, the config and plan value for that attribute will be Unknown if the user didn’t set it. The provider is expected to supply a value, so it’s unknown only until the apply phase.

An attribute cannot be both Null and Unknown.