[THRIFT-2062] cpp flag for using unordered_set instead of set

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Later
• Fix Version/s: 0.9.2
• Component/s: C++ - Compiler
• Assignee: Konrad Grochowski
• Reporter: Vitali Lovich
• Created: 24/Jun/13 17:11
• Updated: 30/Oct/14 03:10
• Resolved: 09/Oct/14 14:47

Description

It would be nice if the cpp compiler could generate code to use unordered_set instead of set. unordered_set is faster & usually an unordered_set is wanted rather than an ordered one. Furthermore, since unordered_set only needs a hash function, we could generate one for every type.

The hash code generated can be along the lines of what Eclipse does for auto-generated hash codes:

struct ThriftObj {
1: string f1;
2: i32 f2;
3: SomeOtherThriftObj f3;
}

// header file:
namespace std {
template <> struct hash<ThriftObj>

{ size_t operator()(const ThriftObj& o); }

}

// cpp file:
namespace std {
template <> struct hash<ThriftObj>

{ size_t operator()(const ThriftObj& o) constexpr size_t prime = 31; size_t hashcode = 1; hashcode += o.__isset.f1 ? prime * std::hash<decltype(o.f1)>()(o.f1) : 0; hashcode += o.__isset.f2 ? prime * std::hash<decltype(o.f1)>()(o.f2) : 0; hashcode += o.__isset.f3 ? prime * std::hash<decltype(o.f1)>()(o.f3) : 0; }

}
}

Issue Links

• relates to: THRIFT-2717 C++V2 generator/library