[interfacekit] Re: How backwards compatible?
- From: "Erik Jaesler" <erik@xxxxxxxxxxxxxx>
- To: interfacekit@xxxxxxxxxxxxx
- Date: Sat, 27 Jul 2002 08:05:18 -0700
My only suggestion with regard to this is to not code in such as way as
to *preclude* adding R3 compatibility later, if need be.
e
>I am working on BPropertyInfo and I have run into a minor issue. I
>have a plan to address it, but I want to check with some people on the
>mailing list first.
>
>Prior to R4, the struct property_info structure had only five elements
>to it. With R4, the structure was changed and three new elements were
>added to it. This means that code that pass a property_info to a
>BPropertyInfo class using the old header from R3 will have a different
>size structure than what is found in R4.
>
>To handle this, Be changed the constructor for BPropertyInfo. The old
>R3 constructor was moved so it became private. However, existing
>binaries will still use this private constructor and this constructor
>knows the structure passed in is the old format and it converts it to
>the new structure. Any code compiled on R4 or newer will use a new
>constructor. Because it is compiled on R4 or later, the right
>property_info structure and BPropertyInfo constructor gets called.
>
>So, the question becomes should I bother to implement the code to
>convert between the old property_info structure and the new one (as of
>R4) and implement this private constructor. Here are the things I have
>considered:
>
>- On Intel, R4 was incompatible with R3. So, all current Intel BeOS
>binaries should not be using the old constructor/old structure format.
>I have checked all ELF files on my BeOS machine and confirmed that none
>of them link against this deprecated constructor. From this
>perspective it should be safe not to implement it.
>
>- On PPC, R4 is compatible with R3. If OpenBeOS is to be compatible
>with PPC in the future, we will need this constructor etc in order to
>run PPC binaries from R3. Personally, I think this isn't too likely.
>If we do end up with a PPC version of OpenBeOS, I suspect it will not
>be compatible at all and be based on the gcc toolchain.
>
>- I am worried that there may be flattened R3 BPropertyInfo's out there
>on someones harddisk, even on Intel. Perhaps Be handled unflattening
>these also. If we don't implement support for old BPropertyInfo
>unflattening, we may have some minor compatibility issues. I think the
>risk here is very low however.
>
>Given all of this, I have decided _not_ to implement this backward
>compatibility to the R3 BPropertyInfo interface. If anyone has any
>concerns about this, please let me know. Thanks.
>
>--
>Jeremy Rand
>jrand@xxxxxxxx
Necessity is the plea for every infringement of human freedom. It is the
argument of tyrants; it is the creed of slaves.
-William Pitt, British prime-minister (1759-1806)
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