Initialize big object header properly#269
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Prevent uninitialized memory from causing an assertion failure.
nickrobinson251
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Dec 9, 2025
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Introduces the `typegroup` syntax that allows multiple type definitions to reference each other cyclically, solving a limitation dating back to 2011 (issue #269). The fundamental construct uses a `typegroup` block: ```julia typegroup struct Node edges::Vector{Edge} end struct Edge from::Node to::Node end end ``` See the documentation for further examples. The fundamental semantics here are that all (mutable) struct definitions within the block have their names introduced at the top of the block and then get created as a unit (constructor definitions are deferred until all types are defined). There was significant discussion about the correct semantics for this (see JuliaLang#60569), but what we ended up with is that there is that before the types are created, the type names are `TypeVar`s and there's a special new `TypeApp` that represents lazy type application (which is not otherwise part of our Type algebra). Instantiation, everything then gets resolved together. Fixes #269 Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com> Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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PR Description
Prevent uninitialized memory from causing an assertion failure.
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