point of defn and default and default arguments

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2 total messages Started by Tony Cook Mon, 07 Aug 1995 07:21

#1665

Author: Tony Cook
Date: Mon, 07 Aug 1995 07:21

42 lines
1366 bytes

Is the following legal:

class T
{
  public:
    T() {}
    // 
    T(int, 
      T const &def_ = T() // note this - use before end of class
    ) { }
};

int main()
{
    T t(0);

    return 0;
}

Why it might be legal:
    default arguments are evaluated at the point of use.

[dcl.fct.default]
9 Default  arguments  are  evaluated  at each point of call before entry
  into a function.

Why it might not be legal:
    names for default arguments are bound at point of declaration,
and T is not fully defined where the default argument is declared.

[dcl.fct.default]
5 Default argument expressions have their names bound  and  their  types
  checked at the point of declaration.

[class] p2
                                                                       A
  class is considered defined after the  closing  brace  of  its  class-
  specifier  has  been seen even though its member functions are in gen-
  eral not yet defined.
-- 
        Tony Cook - tony@online.tmx.com.au
                    100237.3425@compuserve.com

Re: point of defn and default and default arguments

#1685

Author: James Kanze US/ESC 60/3/141 #407...
Date: Wed, 09 Aug 1995 08:48

56 lines
2188 bytes

In article <DCxJ3u.A96@online.tmx.com.au> tony@online.tmx.com.au (Tony
Cook) writes:

|> Is the following legal:

It's legal.

|> class T
|> {
|>   public:
|>     T() {}
|>     // 
|>     T(int, 
|>       T const &def_ = T() // note this - use before end of class
|>     ) { }
|> };

|> int main()
|> {
|>     T t(0);

|>     return 0;
|> }

|> Why it might be legal:
|>     default arguments are evaluated at the point of use.

|> [dcl.fct.default]
|> 9 Default  arguments  are  evaluated  at each point of call before entry
|>   into a function.

Correct.

|> Why it might not be legal:
|>     names for default arguments are bound at point of declaration,
|> and T is not fully defined where the default argument is declared.

|> [dcl.fct.default]
|> 5 Default argument expressions have their names bound  and  their  types
|>   checked at the point of declaration.

|> [class] p2
|>                                                                        A
|>   class is considered defined after the  closing  brace  of  its  class-
|>   specifier  has  been seen even though its member functions are in gen-
|>   eral not yet defined.

Binding a name does not require a complete type.  In fact,
technically, it doesn't require any semantic information concerning
the name.  (In practice, there is no way for you to make a name known
to the compiler without providing some semantic information.)
-- 
James Kanze         Tel.: (+33) 88 14 49 00        email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs-Bourgeois, F-67000 Strasbourg, France
Conseils en informatique industrielle --
                              -- Beratung in industrieller Datenverarbeitung

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