[cfe-dev] Question regarding error

[Douglas Gregor]

On Apr 30, 2010, at 4:55 PM, John Thompson wrote:

> This doesn't compile.  Should it?:
>  
> class test
> {
> public:
>  test( float x );
>  test(__attribute__((vector_size(16))) float v );
> };
> int vi = 0;
> void func()
> {
>  test object = test(vi);
> }
> C:\Sony\Clang\exp>clang -cc1 scalar.cpp
> scalar.cpp:13:16: error: functional-style cast from 'int' to 'test' is not allowed
>         test object = test(vi);
>                       ^~~~

The logic for computing implicit conversion sequences in C++ does not know anything about vectors. What you're seeing here is a poor diagnostic due to the cast. Change it to a direct initialization and you'll see the ambiguity:

t2.cpp:10:7: error: call to constructor of 'test' is ambiguous
 test object(vi);
      ^      ~~
t2.cpp:4:2: note: candidate constructor
 test( float x );
 ^
t2.cpp:5:2: note: candidate constructor
 test(__attribute__((vector_size(16))) float v );
 ^
t2.cpp:1:7: note: candidate is the implicit copy constructor
class test
      ^

Clang can't figure out which constructor is the better match.

	- Doug