implicit conversions and const rvalues

GCC accepts the code below. Clang rejects it. Who is right?

struct ovrMatrix4f {

};

class Matrix4 {

public:

operator const ovrMatrix4f () const {

ovrMatrix4f result;

return result;

}

};

void ok() {

Matrix4 from;

ovrMatrix4f to = from; // that one is fine

}

void bad() {

Matrix4 from;

ovrMatrix4f to;

to = from; // compilation fails here

}

Clang says:

test.cpp:20:8: error: no viable conversion from ‘Matrix4’ to ‘ovrMatrix4f’

to = from; // compilation fails here

^~~~

test.cpp:1:8: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from ‘Matrix4’ to

‘const ovrMatrix4f &’ for 1st argument

struct ovrMatrix4f {

^

test.cpp:1:8: note: candidate constructor (the implicit move constructor) not viable: no known conversion from ‘Matrix4’ to

‘ovrMatrix4f &&’ for 1st argument

struct ovrMatrix4f {

^

test.cpp:6:3: note: candidate function

operator const ovrMatrix4f () const {

^

test.cpp:1:8: note: passing argument to parameter here

struct ovrMatrix4f {

^