From 867ed90e8e5cf9502b60b3459f9bc478232e9234 Mon Sep 17 00:00:00 2001 From: Danilo Piparo Date: Thu, 1 Jan 2026 14:16:58 +0100 Subject: [PATCH] Mention the meaning of class version zero --- manual/io_custom_classes/index.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/manual/io_custom_classes/index.md b/manual/io_custom_classes/index.md index b4b9b0ba..2028c096 100644 --- a/manual/io_custom_classes/index.md +++ b/manual/io_custom_classes/index.md @@ -207,7 +207,7 @@ For more information on TTree, see [Trees]({{ '/manual/trees' | relative_url }}) ## The `ClassDef` macro -The `ClassDef` macro can be inserted in a class definition to add some reflection capabilities to it. It also attaches a "version number" to the class that can be used for [schema evolution]({{ '/manual/io/#dealing-with-changes-in-class-layouts-schema-evolution' | relative_url }}). +The `ClassDef` macro can be inserted in a class definition to add some reflection capabilities to it. It also attaches a "version number" to the class that can be used for [schema evolution]({{ '/manual/io/#dealing-with-changes-in-class-layouts-schema-evolution' | relative_url }}). A class "version number" equal to zero signals that the class cannot be written. Having a `ClassDef` is mandatory for classes inheriting from `TObject`, otherwise it is an optional ROOT I/O performance optimization.