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Revert "Revert "Use template structs instead of phantoms""

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This is the more typically way to do [Argument-dependent
lookup](https://en.cppreference.com/w/cpp/language/adl)-leveraging
generic serializers in C++. It makes the relationship between the `read`
and `write` methods more clear and rigorous, and also looks more
familiar to users coming from other languages that do not have C++'s
libertine ad-hoc overloading.

I am returning to this because during the review in
https://github.com/NixOS/nix/pull/6223, it came up as something that
would make the code easier to read --- easier today hopefully already,
but definitely easier if we were have multiple codified protocols with
code sharing between them as that PR seeks to accomplish.

If I recall correctly, the main criticism of this the first time around
(in 2020) was that having to specify the type when writing, e.g.
`WorkerProto<MyType>::write`, was too verbose and cumbersome. This is
now addressed with the `workerProtoWrite` wrapper function.

This method is also the way `nlohmann::json`, which we have used for a
number of years now, does its serializers, for what its worth.

This reverts commit 45a0ed82f0. That
commit in turn reverted 9ab07e99f5.
This commit is contained in:
John Ericson 2023-05-17 22:04:59 -04:00
parent 684e9be8b9
commit cb5052d98f
10 changed files with 182 additions and 151 deletions
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4
src/libstore/path-info.cc
View file

@ -131,7 +131,7 @@ ValidPathInfo ValidPathInfo::read(Source & source, const Store & store, unsigned
auto narHash = Hash::parseAny(readString(source), htSHA256);
ValidPathInfo info(path, narHash);
if (deriver != "") info.deriver = store.parseStorePath(deriver);
info.references = worker_proto::read(store, source, Phantom<StorePathSet> {});
info.references = WorkerProto<StorePathSet>::read(store, source);
source >> info.registrationTime >> info.narSize;
if (format >= 16) {
source >> info.ultimate;
@ -152,7 +152,7 @@ void ValidPathInfo::write(
sink << store.printStorePath(path);
sink << (deriver ? store.printStorePath(*deriver) : "")
<< narHash.to_string(Base16, false);
worker_proto::write(store, sink, references);
workerProtoWrite(store, sink, references);
sink << registrationTime << narSize;
if (format >= 16) {
sink << ultimate