Add static parameters to custom validator functions?

[timvisee]

I'm looking for a way to add additional parameters to custom validator functions. For example:

struct ExampleStruct {
    #[validate(custom(function = "custom_range", params = "(1, 128)"))]
    name: String,
    #[validate(custom(function = "custom_range", params = "(4, 32)"))]
    alias: String,
}

fn custom_range(value: &String, params: (u64, u64)) -> Result<(), ValidationError> {
    // Some logic here...
}

This would be much better than having a separate function for each configuration such as custom_range_1_128 and custom_range_4_32.

This is different than the arg = "(i32, i32)" feature, because arg is to attach references to external data during validation with validate_args(...). Instead I'd like to specify static parameters inside the struct definitions itself.

Is something like this currently possible? If not, can I submit a PR to implement this?

Note: I understand that in this example the built-in range validator would suffice. I'm just using range as easy to understand example rather than the more complex case I'm currently dealing with.

[Keats]

Why limit it to static? I can bet 2 seconds after this is released someone will want references

[timvisee]

The point is to provide additional parameters to custom validators. Using arg with external references is not an option in our case, partially because we use deeply nested structs.

I meant static as in hardcoded within the validate attribute definition. Yes, that is something we're looking for in our case. That is to prevent boilerplate like this:

https://github.com/qdrant/qdrant/blob/79ba0c95db5d60bf20c8583b4d0651b1bf8e7e76/lib/api/src/grpc/validate.rs#L90-L156