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This release contains bug fixes only. This includes 6 fixes for ARC (memory manager), which was previously not considered ready for serious use due to stability issues.
ARC uses referencing counting instead garbage collection (which most other memory management options for Nim implement). According to the Nim docs this allows for “deterministic performance for hard realtime systems”. ARC was introduced in v1.2.
Another noteworthy fix is for the Nim documentation generator (nim doc) which was broken in v1.2.