JuliaLang/julia

== for immutables should recursively call == on its fields

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#4,648 opened on Oct 26, 2013

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 (60 comments) (44 reactions) (1 assignee)Julia (48,709 stars) (5,773 forks)batch import
breakingequalityhelp wantedneeds decision

Description

This doesn't make much sense:

julia> immutable Foo{T}
         bar::T
       end

julia> Foo("baz") == Foo("baz")
false

julia> Foo("baz").bar == Foo("baz").bar
true

julia> Foo(1) == Foo(1)
true

If the fields are == to each other then the objects should be == to each other.

Contributor guide

Tech stack
None
Domain
backend
Issue type
bug
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.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Julia immutable typesJulia's == operator behaviorRecursive comparison
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
The issue indicates that for immutable types, the == operator currently compares by identity rather than by field values. The fix would involve modifying the definition of == for immutable structs to recursively compare each field using ==. Relevant files likely include the base definition of == in Julia's core library, possibly in 'base/operators.jl' or similar. The discussion in the 60 comments may provide insights into potential implementation strategies and edge cases.