# World Age Problem Explanation

**URL:** <https://discourse.julialang.org/t/world-age-problem-explanation/9714>\
**Category:** General Usage\
**Tags:** world\_age\
**Created:** [March 14, 2018, 12:33pm UTC](https://discourse.julialang.org/t/world-age-problem-explanation/9714 "2018-03-14T12:33:07Z")\
**Posts on this page:** 1\
**Showing post:** 8

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**Author:** ![StefanKarpinski](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stefankarpinski/32/24_2.png) [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)\
**Post date:** [March 16, 2018, 7:21pm UTC](https://discourse.julialang.org/t/world-age-problem-explanation/9714/8 "2018-03-16T19:21:01Z")

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I would add that requiring modifications to dispatch to take effect immediately is one of those classic behaviors in dynamic languages that makes them hard/impossible to compile without heroic efforts (along with reified local scopes, the ability to add state to objects dynamically at any point, etc. – we should make a list some time). In Julia we’re nipping that one in the bud by defining the language to work in a way that can be implemented in the presence of compilation without insane contortions, namely with world ages that only take effect at the top-level, just the way that @kristoffer.carlsson described.

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