Suggestion: default keyword in struct definitions

[nicoburns]

This is an alternative to the #[optional(your_default_value_goes_here)] syntax. Instead struct definition could be name: Type default your_default_value_goes_here.

For example:

enum QuxKinds {
    A,
    B,
    C,
}

struct FooArguments {
    bar: String,
    baz: Option<String> default None,
    qux: QuxKinds       default QuxKinds::A,
}

which could then be instantiated (for example) in the following ways:

FooArguments {bar: "abc".to_owned()}
FooArguments {bar: "abc".to_owned(), baz: Some("cde".to_owned())}
FooArguments {bar: "abc".to_owned(), qux: QuxKinds::B}
FooArguments {bar: "abc".to_owned(), baz: None, qux: QuxKinds::B}

This would require a contextual default keyword, but I believe that wouldn't be problematic given that nothing was valid in that context previously.