JuliaDynamics/Agents.jl

add_agent!() adds agents with out-of-bounds coordinates despite BoundsError

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#1193 opened on Jan 13, 2026

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bugdiscretegood first issue

Description

Describe the bug When add_agent!() is called with out-of-bounds coordinates on a GridSpace, it throws a BoundsError but still adds the agent to the model's dictionary. This creates an inconsistent state where the agent exists in the model but it has an invalid position. Functions such as nearby_ids() do not return this agent's id. I have not tested with other functions though.

Minimal Working Example

using Agents

@agent struct Customer(GridAgent{2}) 
    age
end

space = GridSpace((100,100); periodic = false, metric = :euclidean)
model = StandardABM(Customer, space)
add_agent!((0,0), model,25) #similar behavior when using negative coordinates

Output:

BoundsError: attempt to access 100×100 Matrix{Vector{Int64}} at index [0, 0]

However when checking the agents in the model the agent has been added

allagents(model)

Output:

ValueIterator for a Dict{Int64, Customer} with 1 entry. Values:
  Customer(1, (0, 0), 25)

Agents.jl version

Agents v6.2.10

Contributor guide

Tech stack
None
Domain
data
Issue type
bug
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.
under 1 hour
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.
clear
Prerequisites
Julia programmingAgents.jl basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80
Research direction
The issue is in the `add agent!` function for `GridSpace`, likely defined in `src/core/space.jl` or similar. The fix should validate coordinates before attempting to add the agent to the model's dictionary, ensuring that if `BoundsError` would be thrown, the agent is not added. Additionally, a unit test should be written to verify that adding an agent with out of bounds coordinates does not leave the model in an inconsistent state. Refer to the issue's minimal working example and the existing tests in `test/` for guidance.