Improvement Summary

Rust functions don't have named arguments, and each argument is required.

fn foo(x: u64, y: bool) { ... }

But this is a bit annoying when we are writing tests with default values or fixtures. To have optional named arguments in Rust, we need to create an argument struct and pass it.

fn foo(FooArgs { x: u64, y: bool }) { ... }

Untill now, we didn't have any proper macro library that avoid this code bloat. Currently, in our tests, (mainly in ibc-testkit) we manually define these structs and auto-derive a Builder pattern using typed-builder.

#[typed_builder::TypedBuilder]
struct FooArgs { x: u64, y: bool }

foo(FooArgs::builder().x(x).y(y).build())

Proposal

Recently, there is a new library called bon which offers solutions to this exact problem.

#[bon::builder]
fn foo(x: u64, y: bool) { ... }

foo().x(x).y(y).call()

bon checks arguments at compile time, just like typed-builder.