Comments (3)
My pattern for doing this is to:
- Annotate fields using the serde
default
feature support, annoying but it works :) - Instantiate the figment with
let figment = Figment::from(Serialized::defaults(MyConfig::default()))
and later merge with the other config providers
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If you don't want to use serde's default attribute, nor create a secondary struct, the simplest option, albeit unsatisfying, is to merge the default values into a Figment
manually:
Figment::new()
.merge(Serialized::default("host", ...))
.merge(Serialized::default("port", ...))
Extracting your type from this Figment (with the desired providers added) would then only require the required field(s).
You could also apply this idea in reserve by serializing your default struct with all of its field into a figment, setting the required fields to None, and then extracting from there.
Unfortunately I don't know of a better solution in Rust. There is unfortunately no way to say "give me a struct with the same fields as this struct expect exclude these," which is what we'd need here. You could theoretically write a procedural derive to accomplish this, though I'm not aware of a crate that does this, and a quick search turned up empty, but perhaps you'd have more luck.
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You could also apply this idea in reserve by serializing your default struct with all of its field into a figment, setting the required fields to None, and then extracting from there.
For this approach, do you mean have default that sets all fields (potentially with some dummy values), then use Serialized::default("port", ...)
to set the override and set required fields to None
?
Unfortunately I don't know of a better solution in Rust.
Yeah, I tried searching myself and it's not an easy thing to search for. I'm also not convinced it would be any cleaner.
I ultimately went with serde's default
feature. Even though it means I have to define functions for every default, it's a scalable pattern. I didn't use Serialized::defaults(...)
though, since that would require all the fields to be set.
Thanks everyone for the input. Always good to confirm I'm not missing the obvious 😄.
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Related Issues (20)
- There's no way to unset an `Option` field from env variables HOT 2
- Support FromStr/Display serialization and deserialization HOT 3
- serde(flatten) breaks metadata propagation in errors HOT 4
- Override values from configuration from CLI HOT 11
- Pattern advice: How to use config file with required field without setting it? HOT 4
- Jail create_file in subdir HOT 2
- Write back to config file. HOT 3
- [FEATURE REQUEST]: Write a jail file with non-utf8 contents
- Preserve Toml File map Order HOT 3
- Deserializing yaml structure with enumeration fails HOT 5
- Allow Value::find to traverse arrays HOT 1
- YAML Nested Values Are Not Usable Via Environment Variables with `Env::split` HOT 2
- Option _not_ to check parent directories for configuration files HOT 1
- [Feature Request] allow to override default name for environment variables HOT 5
- FigmentBuilder
- Clippy and `rustfmt` HOT 2
- Question: Conventions to overwrite nested values with env vars HOT 3
- Question: How to load vector of struct with `Env` provider? HOT 2
- Escaping Jail Error HOT 1
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