define default from constant

[Jeremy Andrews]

I recently switched a project from Structopt to Gumdrop and am generally quite happy with the change. However, one thing I've not been able to figure out how to do is to use a const to define a default value.

Essentially, I define a default port and use this in several places in the code:

/// Constant defining Goose's default port when running a Gaggle.
const DEFAULT_PORT: &str = "5115";

One of the places I was able to use it with structopt was in defining the default value for a couple of run-time configuration options. Is there any way to do this with gumdrop?

For example, if I try this:

    /// Sets port Manager listens on
    #[options(no_short, default = DEFAULT_PORT, meta = "PORT")]
    pub manager_bind_port: u16,

I get the following error:

error: expected literal
    --> src/lib.rs:1945:35
     |
1945 |     #[options(no_short, default = DEFAULT_PORT, meta = "PORT")]
     |                                   ^^^^^^^^^^^^

[Luke Jones]

Just a hunch, but what about returning it from an expr default?

[Jeremy Andrews]

I've reworked my codebase so I set defaults manually when not otherwise set, instead of relying on gumdrop for this. It was not because of this issue, it was because I also allow for configurable default overrides. Therefore this issue can be closed if it's not something on the gumdrop roadmap, as this is no longer a concern for me.