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4feb09e0b3
Takeaways. Try to use "friend" on functions/operators that are frequently overloaded EXCEPT if they are in a templated type that is frequently instantiated. So do not put friends in TMap, TSet, TObjectPtr etc, this will slow down compile times. There is a break-even somewhere and hard to tell where it is but taking a class that is templatized on character type probably don't matter either way and then it is nicer to use a friend since that simplies error messages when compiler can't resolve functions/operators. If it is possible to use member functions instead of friend that is the best option in terms of compile time performance. With c++20 you only have to write operator==(Foo, Bar) and the compiler will automatically provide operator==(Bar, Foo), operator!=(Foo, Bar) and operator!=(Bar, Foo). Changes in this changelist involes * Making operator<< friends in non-template types and not friends in template types * Making operator==/!= members where possible and if not possible moved out if type is a frequently instantiated templated type. #preflight 636970f5376a9cd6a80da54a #rb steve.robb [CL 23038965 by henrik karlsson in ue5-main branch]
88 lines
2.2 KiB
C++
88 lines
2.2 KiB
C++
// Copyright Epic Games, Inc. All Rights Reserved.
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#pragma once
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#include "CoreTypes.h"
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#include "Hash/xxhash.h"
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#include "Misc/Guid.h"
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#include "Serialization/Archive.h"
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#include "UObject/NameTypes.h"
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#include <type_traits>
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namespace UE::DerivedData
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{
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/**
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* A type that builds a build version from arbitrary values serialized to it.
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*
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* FGuid GetVersion() const final
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* {
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* FBuildVersionBuilder Builder;
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* Builder << FGuid(TEXT("a3ae79ff-6a89-4124-afd6-dc095e000488"));
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* Builder << ThirdPartyLibraryVersion;
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* return Builder.Build();
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* }
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*/
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class FBuildVersionBuilder final : public FArchive
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{
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public:
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inline FBuildVersionBuilder();
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inline FGuid Build() const;
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inline FString GetArchiveName() const final { return TEXT("FBuildVersionBuilder"); }
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inline void Serialize(void* Data, int64 Num) final;
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using FArchive::operator<<;
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FArchive& operator<<(FName& Name) final;
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template <typename ArgType>
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inline FBuildVersionBuilder& operator<<(ArgType&& Arg)
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{
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FArchive& Ar = *this;
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Ar << const_cast<std::decay_t<ArgType>&>(Arg);
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return *this;
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}
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private:
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FXxHash128Builder HashBuilder;
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};
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inline FBuildVersionBuilder::FBuildVersionBuilder()
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{
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SetIsSaving(true);
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SetIsPersistent(false);
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// Hash this as the namespace of the Version 3 UUID created in Build().
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static FGuid BaseVersion(TEXT("b9080e6a-9eb2-4c25-8810-e957009fa0a1"));
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HashBuilder.Update(&BaseVersion, sizeof(FGuid));
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}
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inline FGuid FBuildVersionBuilder::Build() const
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{
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FXxHash128 Hash = HashBuilder.Finalize();
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uint32 A = uint32(Hash.HashHigh >> 32);
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uint32 B = uint32(Hash.HashHigh);
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uint32 C = uint32(Hash.HashLow >> 32);
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uint32 D = uint32(Hash.HashLow);
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// Convert to a Variant 1 Version 3 UUID, which is meant to be created
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// by hashing the namespace and name with MD5, but this is using XXH3.
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B = (B & ~0x0000f000) | 0x00003000; // Version 3 (MD5)
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C = (C & ~0xc0000000) | 0x80000000; // Variant 1 (RFC 4122 UUID)
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return FGuid(A, B, C, D);
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}
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inline void FBuildVersionBuilder::Serialize(void* Data, int64 Num)
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{
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HashBuilder.Update(Data, uint64(Num));
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}
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inline FArchive& FBuildVersionBuilder::operator<<(FName& Name)
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{
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FString NameString = Name.ToString();
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return *this << NameString;
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}
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} // UE::DerivedData
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