Should Codec building panic, return Err, or populate default values when missing fields?

[shelbyd]

Given I have the following struct:

struct Foo {
  bar :u32;
  baz :u32;
  qux :u32;
}

I think the API for building should be something like:

let builder = parser.struct_def("Foo").builder();

let object = builder
  .set("bar", 42)
  .set("baz", 43)
  .set("qux", 44)
  .build();

The question is what should happen if we don't set a field and try to build?

It's sometimes a programming error, where panicing makes sense. Possibly there are cases where the programmer can't prevent it from failing (like building from a UI or from JSON)? That would make me want it as a Result, and just have most places unwrap it. We could also fill out all the unspecified fields with default values.

Maybe the best option is 3 different build methods that each do one of the different approaches.

@boymaas @frm Thoughts?

[frm]

I'm a fan of the Elixir & Ruby way of using a different method (usually ending with !) to indicate it panics.

Thinking from the perspective of the data host, I would rather control my logic by checking if it errored, rather than implementing control flow through exceptions.

I recognise the value of having a panic, though, as it removes any overhead code handling the return of an error. My take is then to have different build methods and suit the potential use cases.

[shelbyd]

I think we'll go with:

• build - panics with missing fields
• try_build - returns a Result<Object, Error>
• build_or_else - calls a closure for missing fields