`#[debug(skip_if = "condition")]` functionality

[MrFoxPro]

Example:

use derive_more::Debug;

#[derive(Debug)]
struct A {
	#[debug(skip_if = "Option::is_none")]
	pub b: Option<u32>
}

[tyranron]

@MrFoxPro frankly, for me this seems to be quite a specific feature, that worth providing manual implementation rather than supporting in derive_more::Debug.

I would like to collect more feedback on this, whether it's something a lit bit more widely wanted by users, before deciding whether to add this or not.

[iliakonnov]

In my use case I have a bunch of structs, each having many optional attributes that are very rarely set.

For example, I have a following struct for describing a single entry in a nftables set:

struct SetEntry<K, V> {
    key: K,
    value: V,
    userdata: Option<Vec<u8>>,  // read as "comment", often missing, especially on set items
    timeout: Option<Duration>,  // used only whenever you want sets with expiring items
    expiration: Option<Duration>,  // same as `timeout`
    expressions: Vec<Expression>,  // maps may contain stateful objects, which is not really known feature
    flags: nftables::SetElemFlags,  // may store `CatchAll` flag, which is not really documented anywhere
}

This struct has two mandatory fields and five optional fields, most of which are never set on normal systems.

I have dozens of items in my sets and I would like to not see five different None values each time I'm printing every single one of them.