"name"_a=name, "number"_a=number);
What is the ""_a= doing?
"name"_a=name, "number"_a=number);
What is the ""_a= doing?
""_a is a user defined literal.
In this context it would help you create the equivalent arg("name", value) by writing it as "name"_a = value.
However the named arguments didn't make it into the standard so this is not part of the standrd lib. You could still write it if you really wanted to.