[Refactor] Fix some -Wdeprecated-copy warnings #2089
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Also remove unneeded swap func in SignedMessage
CFeeRate and CTxMemPoolEntry have explicitly defined copy ctors which has the same functionality as the implicit default copy ctors which would have been generated otherwise. Besides being redundant, it violates the rule of three (see https://en.wikipedia.org/wiki/Rule_of_three_(C%2B%2B_programming) ). (Of course, the rule of three doesn't -really- cause a resource management issue here, but the reason for that is exactly that there is no need for an explicit copy ctor in the first place since no resources are being managed). CFeeRate has an explicitly defined copy ctor which has the same functionality as the implicit default copy ctor which would have been generated otherwise.
furszy
approved these changes
Dec 21, 2020
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Fix the
-Wdeprecated-copywarnings listed in #2076Background
While perfectly valid in C++98, implicit generation of the copy constructor is declared as deprecated in C++11, when there is already a user-defined copy assignment operator, or vice-versa.
The rationale behind this is the "rule of three" (https://en.cppreference.com/w/cpp/language/rule_of_three)
Issue - Fix
We have several places that define redundant copy assignment operators (and then use the implicit copy constructor), or that do need non-default ctors/dtors but don't define copy assignment.
(See also bitcoin#11161, which is also cherry-picked here)
Specifically:
CSignedMessage/CMasternodePing/CMasternodeuse a weird copy-assignment that swaps with the argument (which, of course, cannot be "const" then). Here we remove all ::swap implementations, and provide actual copy assignment operators.CTransactionhas an explicit copy-assignment operator, but uses the implicit copy-ctor inCMerkleTxconstructor.CFeeRateandCTxMemPoolEntryhave explicitly defined copy ctor, which can (and should, for the rule-of-three) be replaced by the default one (Remove redundant explicitly defined copy ctors bitcoin/bitcoin#11161).Note
Reason why these warnings pop up just now.
Since Clang 10.0 and GCC 9.3,
-Wextraenables-Wdeprecated-copyby default, and that is very spammy, especially when compiling with the QT GUI (bitcoin#15822 / bitcoin#18419).It is so spammy (also with
boost-1.72.0) that Bitcoin decided to temporarily suppress this warning (bitcoin#18738) until QT fixes it upstream, and boost is definitely removed in 0.22 (bitcoin#18967)