Home/ Questions/Q 8770891
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-13T17:39:03+00:00

For a class Foo, is there a way to disallow constructing it without giving

  • 0

For a class Foo, is there a way to disallow constructing it without giving it a name?

For example:

Foo("hi");

And only allow it if you give it a name, like the following?

Foo my_foo("hi");

The lifetime of the first one is just the statement, and the second one is the enclosing block. In my use case, Foo is measuring the time between constructor and destructor. Since I never refer to the local variable, I often forget to put it in, and accidentally change the lifetime. I’d like to get a compile time error instead.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Another macro-based solution:

    #define Foo class Foo

    The statement Foo("hi"); expands to class Foo("hi");, which is ill-formed; but Foo a("hi") expands to class Foo a("hi"), which is correct.

    This has the advantage that it is both source- and binary-compatible with existing (correct) code. (This claim is not entirely correct – please see Johannes Schaub’s Comment and ensuing discussion below: “How can you know that it is source compatible with existing code? His friend includes his header and has void f() { int Foo = 0; } which previously compiled fine and now miscompiles! Also, every line that defines a member function of class Foo fails: void class Foo::bar() {}”)

    • 0