[llvm-dev] C++ compiler error I do not understand

[Paul C. Anagnostopoulos via llvm-dev]

I have the following situation with which I could use some 
enlightenment. As usual, the context is TableGen.

in class Record:

    public:
       using AssertionTuple = std::tuple<SMLoc, Init *, Init *>;
    ...
       SmallVector<AssertionTuple, 0> Assertions;

then there exists:

       struct RecordsEntry {
         std::unique_ptr<Record> Rec;
         std::unique_ptr<ForeachLoop> Loop;
         std::unique_ptr<Record::AssertionTuple> Assertion;

         void dump() const;

         RecordsEntry() {}
         RecordsEntry(std::unique_ptr<Record> Rec) : Rec(std::move(Rec)) {}
         RecordsEntry(std::unique_ptr<ForeachLoop> Loop)
           : Loop(std::move(Loop)) {}
         RecordsEntry(std::unique_ptr<Record::AssertionTuple> Assertion)
    // 4th constructor
           : Assertion(std::move(Assertion)) {}
       };

    ...

    bool TGParser::addEntry(RecordsEntry E) { ...

Note that I expect to create a RecordsEntry by passing an AssertionTuple 
to addEntry and having the 4th constructor do the trick. The other three 
constructors all work fine. However, when I do this:

         Record::AssertionTuple tuple = std::make_tuple(ConditionLoc,
    Condition, Message);
         addEntry(std::move(tuple));

I get this:

    C:\LLVM\llvm-project\llvm\lib\TableGen\TGParser.cpp(3190): error
    C2664: 'bool llvm::TGParser::addEntry(llvm::RecordsEntry)': cannot
    convert argument 1 from 'llvm::Record::AssertionTuple' to
    'llvm::RecordsEntry'
    C:\LLVM\llvm-project\llvm\lib\TableGen\TGParser.cpp(3190): note: No
    user-defined-conversion operator available that can perform this
    conversion, or the operator cannot be called
    C:\LLVM\llvm-project\llvm\lib\TableGen\TGParser.cpp(344): note: see
    declaration of 'llvm::TGParser::addEntry'

Ah, I guess I should show the definitions of the three arguments passed 
to make_tuple() above:

       SMLoc ConditionLoc = Lex.getLoc();
       Init *Condition = ParseValue(CurRec);
       Init *Message = ParseValue(CurRec);

Since there is no complaint about making the tuple, I assume those three 
arguments have the correct type. The problem is the 4th RecordsEntry 
constructor, which cannot convert the addEntry argument 
'std::move(tuple)' to a Record::AssertionTuple, even though that's 
exactly what it is.

P.S.: Regardless of what I learn here, I'm going to change the assertion 
tuple into a little struct, which should work fine as demonstrated by 
constructor 3 above.


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