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Clarify that (Flat|Flex)Buffers do not deduplicate vector elements (#6415)

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I'm also clarifying that while elements are not deduplicated, vectors
may contain more than one offset to the same value.

Signed-off-by: Juan Cruz Viotti <jv@jviotti.com>
This commit is contained in:
Juan Cruz Viotti
2021-01-21 20:09:35 -04:00
committed by GitHub
parent 7b1ee31d80
commit 796ed68faf
1 changed files with 8 additions and 2 deletions
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10
docs/source/Internals.md
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@@ -88,7 +88,9 @@ They start with an `soffset_t` to a vtable. This is a signed version of
This offset is substracted (not added) from the object start to arrive at This offset is substracted (not added) from the object start to arrive at
the vtable start. This offset is followed by all the the vtable start. This offset is followed by all the
fields as aligned scalars (or offsets). Unlike structs, not all fields fields as aligned scalars (or offsets). Unlike structs, not all fields
need to be present. There is no set order and layout. need to be present. There is no set order and layout. A table may contain
field offsets that point to the same value if the user explicitly
serializes the same offset twice.
To be able to access fields regardless of these uncertainties, we go To be able to access fields regardless of these uncertainties, we go
through a vtable of offsets. Vtables are shared between any objects that through a vtable of offsets. Vtables are shared between any objects that
@@ -124,7 +126,8 @@ Strings are simply a vector of bytes, and are always
null-terminated. Vectors are stored as contiguous aligned scalar null-terminated. Vectors are stored as contiguous aligned scalar
elements prefixed by a 32bit element count (not including any elements prefixed by a 32bit element count (not including any
null termination). Neither is stored inline in their parent, but are referred to null termination). Neither is stored inline in their parent, but are referred to
by offset. by offset. A vector may consist of more than one offset pointing to the same
value if the user explicitly serializes the same offset twice.
### Construction ### Construction
@@ -353,6 +356,9 @@ Since this is an untyped vector `SL_VECTOR`, it is followed by 3 type
bytes (one per element of the vector), which are always following the vector, bytes (one per element of the vector), which are always following the vector,
and are always a uint8_t even if the vector is made up of bigger scalars. and are always a uint8_t even if the vector is made up of bigger scalars.
A vector may include more than one offset pointing to the same value if the
user explicitly serializes the same offset twice.
### Types ### Types
A type byte is made up of 2 components (see flexbuffers.h for exact values): A type byte is made up of 2 components (see flexbuffers.h for exact values):