I think I'm missing something basic regarding the lvalue-to-rvalue standard conversion.
From C++11 4.1:
A glvalue of a non-function, non-array type T can be converted to a prvalue
So we declare a variable x:
int x = 42; An expression x in this scope is now an lvalue (so also a glvalue). It satisfies the requirements in 4.1 for an lvalue-to-rvalue conversion.
What is a typical example of a context where the lvalue-to-rvalue conversion is applied to the expression x?
A prvalue ("pure" rvalue) is an expression that identifies a temporary object (or a subobject thereof) or is a value not associated with any object.
struct Bar { int foo() { int x = 42; return x; // x is converted to prvalue } }; the expression bar.foo() is a prvalue.
OR
Lambda expressions, such as
[](int x){return x*x;} § 3.10.1
A prvalue (“pure” rvalue) is an rvalue that is not an xvalue. [ Example: The result of calling a function whose return type is not a reference is a prvalue. The value of a literal such as 12, 7.3e5, or true is also a prvalue. —end example ]
see n3055.
bar.foo() is that what you meant calling a function? I won't say foo is prvalue. :)const int& a = 10; &a;, there are non-prvalues that directly refer to them aswell, see 15.1p3 "Throwing an exception copy-initializes (8.5, 12.8) a temporary object, called the exception object. The temporary is an lvalue and is used to initialize the variable named in the matching handler".