C++ 11 Curly Braces

Question

I haven't used C++ for a good few years, and have just come across this:

program.build({ default_device }) 

The definition is:

cl_int build(     const VECTOR_CLASS<Device>& devices,     const char* options = NULL,     void (CL_CALLBACK * notifyFptr)(cl_program, void *) = NULL,     void* data = NULL) const 

What are the curly braces there for? I have never seen them used in a function call like this before. I assume it has something to do with the function pointer, but that seems optional?

Answer 1

std::vector has a constructor that takes an std::initializer_list.

An initializer_list can be expressed with curly braces.

So this code creates a vector with one default_device in it and passes it to the build member function.

Answer 2

In:

program.build({ default_device }) 

you are automagically instantiating a temporary VECTOR_CLASS<Device> object. It is equivalent to:

program.build(VECTOR_CLASS<Device>{ default_device }) 

which is equivalent to:

program.build(std::vector<Device>{ default_device }) 

which will call the std::initializer_list constructor:

std::vector::vector(std::initializer_list<T> init,      const Allocator& alloc = Allocator());