delta-io/delta

[Feature Request][Kernel] Support implicit cast for `DefaultExpressionEvaluator` output.

Open

#2,047 opened on Sep 12, 2023

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 (1 comment) (0 reactions) (0 assignees)Scala (8,807 stars) (2,100 forks)batch import
enhancementgood first issuekernel

Description

Feature request

Which Delta project/connector is this regarding?

  • Spark
  • Standalone
  • Flink
  • Kernel
  • Other (fill in here)

Overview

Currently ExpressionHandler.getEvaluator takes an expected output type as argument. The comment here is to handle the implicit cast incase the expression output can be safely cast to the asked output type.

Contributor guide

Tech stack
java
Domain
backend
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.
3-5 days
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
Scala/Java knowledgeDelta Kernel basicsExpression evaluation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
The issue requests support for implicit casting in `DefaultExpressionEvaluator` output. Start by examining `ExpressionHandler.getEvaluator` method and the linked comment in PR #1997 (delta/pull/1997/files#r1312397301). Investigate how the expected output type is currently used and where safe casting could be inserted. Look for existing type conversion utilities in the Delta Kernel codebase. The goal is to implement automatic casting when the expression output type can be safely converted to the requested type.