Syntax help: simplifying initialization of generated structures

[Laurie]

I'm still learning Rust and have just started working with Protobuf definitions via Prost. The definitions are pre-existing (used in a number of projects already) so I can't alter those; I'm looking for help with better / more ideomatic Rust syntax for consuming the structures Prost generates.

In particular, here's a simplification of one scenario I'm dealing with:

#[derive(Default)]
pub struct A {
    id: Option<i64>,
}

#[derive(Default)]
pub struct B {
    parent: Option<A>,
}

#[derive(Default)]
pub struct C {
    parent: Option<B>,
    foo: Option<bool>,
}

...

let c = C { 
    foo: Some(true), 
    ..Default::default() 
}

if let Some(b) = c.parent {
    if let Some(a) = b.parent {
        a.id = Some(999);
    }
}

In initializing c, can I:

• simplify Some(true) (i.e. some sort of auto-boxing?)
• specify grandparent id either:
  a) directly in the struct initializer?
  b) by some terser syntax than the nested if let ... sequence?

[alice]

For your auto-boxing, you can make a constructor. As for the nested if, you can use Option::and_then

if let Some(a) = c.get_parent().and_then(|b| b.get_parent())

Here I've added an get_parent that should return Option<&ParentType>, which you can implement using Option::as_ref.

[Laurie]

Where did you add get_parent, given that the structs A, B and C are Prost generated code (and so can't be modified directly)?

[mbrubeck]

You can add methods to any type by creating your own trait and implementing it for that type.

You can also add inherent methods to a type by putting an impl anywhere in the crate where the type is defined, even in a different module.

[alice]

Impl blocks do not have to be in the same file as the struct definition, so you could just try putting this somewhere?

impl B {
    fn get_parent(&self) -> Option<&A> {
        self.parent.as_ref()
    }
}

[Laurie]

That's very helpful to know, I can tailor the generated API to my taste that way! Thanks!