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@aardappel this looks sensible to me but I'm not entirely sure, can you take a look?

Hmm, this seems a bug indeed, wonder why no-one has ever run into it?

Why not use https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/sizeof ?
The call you're making generally amounts to the same thing, but does type introspection for more complex types of T, would not trust it to be as cheap as the operator.

Also on that link:

The value returned by sizeof can differ from the result of [Marshal.SizeOf(Object)](https://learn.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.marshal.sizeof#system-runtime-interopservices-marshal-sizeof(system-object)), which returns the size of the type in unmanaged memory.

Apparently unmanaged bool can become 4 bytes etc, not corresponding to FlatBuffers types anymore.

@KanouAo can you make a regression test for this? And investigate if sizeof can/should be used instead?

@aardappel

Hmm, this seems a bug indeed, wonder why no-one has ever run into it?

I think not many people have encountered this problem so far because the bug was only introduced on October 25, 2025, by commit 95053e6. This commit changed the meaning of the parameter len in ByteBuffer.ToArray<T> from 'number of Ts' to 'length in bytes', but did not update Table.__vector_as_array<T>, which still calls ToArray<T> with the number of Ts.

Since there were no tests for GetVectorOfLongsArray/GetVectorOfDoublesArray, all tests passed.

I created a PR 2036b0b that adds these tests to FlatBuffersExampleTests.cs and includes a slightly different solution for Table.__vector_as_array<T>. These tests pass before commit 95053e6 and fail with it and succeed again with commit 2036b0b.