Block initialization

[nbenn]

What is meant with initialization? Do we need this? Should we rename this piece of functionality?

Initially, initialization was meant to set up blocks with missing field values using somewhat arbitrary functionality to populate default values. In practice this is rarely useful as it is the user who should input values and pre-populating just causes unnecessary computation.

There still is a step that has not lost relevance like filling in defaults has: evaluating field components that are represented by functions instead of values. This is not only part of initialization, but is also required upon updates.

Maybe we should look at this as

• eval_fields(),
• eval_block()

instead?

Another open question is how eval_fields() should behave for not-yet-initialized blocks. It might be that eval_fields() should run before the user has supplied inputs, but how do we know when it is safe to run eval_fields()? Currently the block implemented is responsible for catching e.g. zero length inputs in their functions. Do we need a special value to signal "input not yet provided"?

[nbenn]

Block evaluation could be conditional on is_initialized(). We currently also here have this behavior where an "uninitialized" filter acts as identity transform. This is not all that useful. It'd be better to just stop evaluation until filter values are chosen by the user.