# \#behavior

**URL:** https://discourse.julialang.org/tag/behavior/145.md

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## [Arceus.jl — A Lightning-Fast Behavior Resolution System](https://discourse.julialang.org/t/arceus-jl-a-lightning-fast-behavior-resolution-system/130321)

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**Author:** [@Gesee](https://discourse.julialang.org/u/Gesee)\
**Replies:** 24\
**Last updated:** [July 3, 2025, 12:12am UTC](https://discourse.julialang.org/t/arceus-jl-a-lightning-fast-behavior-resolution-system/130321 "2025-07-03T00:12:58Z")

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Hi all, I’m happy to present Arceus.jl, a fork of a high-performance AliceRoselia’s original package Arceus, which introduces a novel way to resolve behaviors for entities based on their component sets—using magic bitbo…

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## [SymPy undefined behavior](https://discourse.julialang.org/t/sympy-undefined-behavior/89432)

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**Author:** [@mendeli](https://discourse.julialang.org/u/mendeli)\
**Replies:** 3\
**Last updated:** [October 28, 2022, 12:59pm UTC](https://discourse.julialang.org/t/sympy-undefined-behavior/89432 "2022-10-28T12:59:06Z")

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Being relatively new to Julia, I wrote something like the code below and stumbled on undefined behavior. Since the code below does not use the correct expr.subs() syntax, shouldn’t it issue an error message or warning? T…

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## [Package Parameters, mutable struct as function argument](https://discourse.julialang.org/t/package-parameters-mutable-struct-as-function-argument/47175)

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**Author:** [@cricci](https://discourse.julialang.org/u/cricci)\
**Replies:** 3\
**Last updated:** [September 24, 2020, 6:21am UTC](https://discourse.julialang.org/t/package-parameters-mutable-struct-as-function-argument/47175 "2020-09-24T06:21:44Z")

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I am using the Parameters package to do some work. One of the parameters is an array and surprisingly the struct gets changed when I give it as an argument to a function that modify the array after unpacking using Param…

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## [Don't understand behaviour of NamedTuple{...,Tuple{...,T}} where T](https://discourse.julialang.org/t/dont-understand-behaviour-of-namedtuple-tuple-t-where-t/46382)

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**Author:** [@Graham\_Gill](https://discourse.julialang.org/u/Graham_Gill)\
**Replies:** 6\
**Last updated:** [September 11, 2020, 3:44am UTC](https://discourse.julialang.org/t/dont-understand-behaviour-of-namedtuple-tuple-t-where-t/46382 "2020-09-11T03:44:50Z")

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Here’s an example to enter in the REPL. I don’t understand the behaviour of Z(x) below. I’m using Julia 1.4.2. julia\> Y = NamedTuple{(:a,:b), Tuple{String,Real}} julia\> Z = NamedTuple{(:a,:b), Tuple{String,T}} where T \<…