dotnet/roslyn

Suggestion to use `obj is SomeConst` instead of safe cast or direct Equals(object) call

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#45,232 opened on Jun 16, 2020

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 (5 comments) (0 reactions) (0 assignees)C# (4,257 forks)batch import
Area-IDEConcept-Continuous Improvementhelp wanted

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Description

obj as string == "x" and "x".Equals(obj) would be replaced with obj is "x".

This could apply to all constant types, so obj as bool? == SomeBoolConstant and SomeBoolConstant.Equals(obj) would be replaced with obj is SomeBoolConstant.

When CS0252 "Possible unintended reference comparison; to get a value comparison, cast the left hand side to type 'string'" is reported, this fix could offer to change obj == "x" to obj is "x".

Happy to implement.

Contributor guide

Research direction
Examine existing analyzer and code fix providers for pattern matching (e.g., IDE0074) to understand how to add a new diagnostic and fix for replacing cast or Equals with 'is' pattern. Look at the Roslyn source for similar cases like 'obj is null' or 'obj is string'.
Tech stack
csharp
Domain
developer experiencetooling
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#GitRoslyn
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80