metosin/malli

Feature: Using Java classes as schemas

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#1,007 opened on Feb 2, 2024

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 (5 comments) (1 reaction) (0 assignees)Clojure (1,724 stars) (237 forks)batch import
enhancementhelp wanted

Description

Occasionally, it is necessary to drop down to Java interop. When that happens, I don't want to lose the ease and simplicity of Malli's validation, and I don't want to have to write my own custom :fn schema each time merely to call (instance? SomeClass value).

It would be helpful to have support for recognizing Java classes, effectively wrapping instance? for general use. I looked at the malli.core code and I'm not entirely sure how to accomplish this or I'd offer to do it.

Thanks so much

Contributor guide

Tech stack
java
Domain
backenddata
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Clojure basicsJava interopMalli schema system
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate how Malli registers and handles schema types, particularly custom `:fn` schemas. Look at `malli.core` for the schema dispatch mechanism. To support Java classes, you might need to add a new type or extend existing handling to recognize `Class` objects and generate appropriate validation using `instance?`. Check if there are existing protocols or multimethods for schema creation that can be leveraged.