Using 'override' for a function that has been declared using 'typedef'

C++ 11 introduced the 'override' specifier for functions and I find it useful as it makes it explicit that a virtual function is being overridden. However, I can't seem to get it work for a function that has been declared using a typedef.

I understand that 'override' is not a keyword, has it got something to do with that?

The following code illustrates my point:

#include <iostream>

typedef char ReturnsChar();

class Basic

public:
virtual char get_a();
virtual ReturnsChar get_z;
;

char Basic::get_a() return 'a';
char Basic::get_z() return 'z';

class Capitalized : public Basic

public:
// Can override explicitly if I use the normal definition
char get_a() override;

// Compiles if I use the typedef but not 'override'
ReturnsChar get_z;

// Will not compile, but would like to do this
//ReturnsChar get_z override;

;

char Capitalized::get_a() return 'A';
char Capitalized::get_z() return 'Z';

int main()

Basic foo;
Capitalized bar;

std::cout << foo.get_a() << std::endl; // a
std::cout << foo.get_z() << std::endl; // z
std::cout << bar.get_a() << std::endl; // A
std::cout << bar.get_z() << std::endl; // Z



I'm using GNU's g++ 8.2.0 and the error it gives me is

error: expected ';' at end of member declaration
ReturnsChar get_z override;
^~~~~
;
error: ‘override’ does not name a type; did you mean ‘ctermid’?
ReturnsChar get_z override;
^~~~~~~~
ctermid


EDIT: To address the comments, I understand this style is unclear. I am more interested about why this won't compile and what exactly 'override' does (especially because it is not a keyword).
As an aside, I feel like typedef-ing functions might be clear in some cases, say:

void (*foo(int x, void (*f)(int)))(int);


That's hard to read, especially if comes up often. I can just typedef that as 'UpdateAddressFunction' and then mentally think of every function of that type as something that 'updates an address'.

typedef

get_z

1 Answer
1

I understand that 'override' is not a keyword, has it got something to do with that?

It does: override is only recognised in a few specific contexts and is available as a name for ordinary use otherwise. However, I believe this is a compiler bug, and this is one context where the compiler should recognise it in its special meaning.

override

The relevant grammatical production for this is

[class.mem]

member-declarator:

  declarator virt-specifier-seq_opt pure-specifier_opt

This does not require that a virt-specifier-seq only appear in a declaration containing parameters. The only similar requirement is stated below:

[class.mem]p8:

A virt-specifier-seq shall appear only in the declaration of a virtual member function (10.3).

In your case, the declaration is one of a virtual member function. I believe override should be accepted here.

override

struct A struct B ; struct B override; ;

override

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