I think I have explained my motivation but let me try to make it
clearer.
For example, BIP62 says "scriptPubKey evaluation will be required to
result in a single non-zero value". If we had BIP62 before BIP16, P2SH
could not be done in the current form because BIP16 leaves more than one
element on the stake for non-upgrading nodes. BIP17 also violates BIP62.
BIP68 is "only enforced if the most significant bit of the sequence
number field is set.", so it is optional, anyway. All I do is to move
the flag from sequence number to version number.
The blocksize debate shows how a permanent softfork may cause trouble
later. We need to be very careful when doing further softforks, making
sure we will have enough flexibility for further development.
Mark Friedenbach 於 2015-08-08 14:56 寫到:
It is not a bug that you are unable to selectively choose these
features with higher version numbers. The version selection is in
there at all because there is a possibility that there exists already
signed transactions which would violate these new rules. We wouldn't
want these transactions to become unspendable. However moving forward
there is no reason to selectively pick and choose which of these new
consensus rules you want to apply your transaction.
On Aug 8, 2015 11:51 AM, "jl2012 via bitcoin-dev"
<bitcoin-dev@lists.linuxfoundation.org> wrote:
BIP68 rules and some of the BIP62 rules are applied only if the tx
version is >=2 and >=3 respectively. Therefore, it is not possible
to create a tx which follows BIP62 but not BIP68. If we introduce v4
tx later, BIP62 and BIP68 will all become mandatory.
Some rules, e.g. "scriptPubKey evaluation will be required to
result in a single non-zero value" in BIP62, will cause trouble when
we try to introduce a new script system with softfork.
I suggest to divide the tx version field into 2 parts: the higher 4
bits and lower 28 bits.
BIP62 is active for a tx if its highest bits are 0000, and the
second lowest bit is 1.
BIP68 is active for a tx if its highest bits are 0000, and the
third lowest bit is 1.
So it will be easier for us to re-purpose the nSequence, or to take
advantage of malleability in the future. If this is adopted, the
nSequence high bit requirement in BIP68 becomes unnecessary as we
could easily switch it off.
The low bits will allow 28 independent BIPs and should be ample for
many years. When they are exhausted, we can switch the high bits to
a different number (1-15) and redefine the meaning of low bits. By
that time, some of the 28 BIPs might have become obsoleted or could
be merged.
(I'm not sure if there are other draft BIPs with similar
interpretation of tx version but the comments above should also
apply to them)
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