Add `unique` constraint to list?

[samuelcolvin]

I'm not sure about this, it would need to have minimal or no impact on performance when switched off.

Some questions if we are to support it:

• Should we implement unique only on the list validator or on tuple, set, frozenset and general iterables as we build the vec?
• Should we implement a unique check on set and frozenset validators - this would have minimal performance impact as it would involve simply checking that the length of the input before and after creating the set, but sets loose order so won't be sufficient for some scenarios
• what's the most performant way to implement this in rust??? I guess for list[int] and a few other types, we could do something pretty performant with an AHashSet but a general case will require some fairly slow python.

[odiseo0]

I may be confused but, why set and frozenset? Those collections doesn't allow for duplicate values.

About the unique implementation, would it be compared by equality or by identity?

[samuelcolvin]

equality.

I may be confused but, why set and frozenset? Those collections doesn't allow for duplicate values.

Well, the question is whether [1, 2, 2, 3] as input to a set should raise an error - I think that's a useful option, but doesn't solve all problems since sets loose order.

[odiseo0]

Ok, I understood. I think it's okay and is up to the developer whether to use it or not.

I'll try to do an implementation as a draft or as a reference.

[samuelcolvin]

Great, thank you.

[ybressler]

Ok, I understood. I think it's okay and is up to the developer whether to use it or not.

I'll try to do an implementation as a draft or as a reference.

Q: You are doing this in python? Or rust? (Asking out of curiosity >> I want to learn how this stuff works.)

[samuelcolvin]

this needs to be in rust since the list validator is all written in rust, see

pydantic-core/src/validators/list.rs

Line 96 in 9e54f78

impl Validator for ListValidator {

[sasanjac]

After the removal of unique_items in v2 and this issue there is no way in v2 to specify a unique array when serializing the model.

[PaarthShah]

After the removal of unique_items in v2 and this issue there is no way in v2 to specify a unique array when serializing the model.

Yeah, this one was an unfortunate loss for me; I just want a List[T] with unique, sorted elements.