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digitalmars.D.learn - UDA example

reply "Craig Dillabaugh" <cdillaba cg.scs.carleton.ca> writes:
When I attempt to compile the following example code from the
section on UDAs
at:  http://dlang.org/attribute.html

void main(string args[]) {
template Tuple (T...)
{
          alias T Tuple;
}

enum EEE = 7;
 ("hello") struct SSS { }
 (3) {  (4)  EEE  SSS int foo; }

alias Tuple!(__traits(getAttributes, foo)) TP;

pragma(msg, TP); // prints tuple(3, 4, 7, (SSS))
pragma(msg, TP[2]); // prints 7
}

I get the following errors:

UDAs.d(9): Error: basic type expected, not {
UDAs.d(9): Error: no identifier for declarator int
UDAs.d(9): Error: semicolon expected, not '{'

Line 9 is the one starting " (3) ..."

Is this due to:
         a. a DMD bug (DMD64 D Compiler v2.063.2, Linux)
         b. a Documentation bug
         c. me not properly copying/pasting the example :/

Craig

P.S. This reCAPTCHA anti-spam think sucks.
Aug 19 2013
parent reply Jacob Carlborg <doob me.com> writes:
On 2013-08-19 19:57, Craig Dillabaugh wrote:

 When I attempt to compile the following example code from the
 section on UDAs
 at:  http://dlang.org/attribute.html

 void main(string args[]) {
 template Tuple (T...)
 {
           alias T Tuple;
 }

 enum EEE = 7;
  ("hello") struct SSS { }
  (3) {  (4)  EEE  SSS int foo; }

 alias Tuple!(__traits(getAttributes, foo)) TP;

 pragma(msg, TP); // prints tuple(3, 4, 7, (SSS))
 pragma(msg, TP[2]); // prints 7
 }

 I get the following errors:

 UDAs.d(9): Error: basic type expected, not {
 UDAs.d(9): Error: no identifier for declarator int
 UDAs.d(9): Error: semicolon expected, not '{'

 Line 9 is the one starting " (3) ..."

 Is this due to:
          a. a DMD bug (DMD64 D Compiler v2.063.2, Linux)
          b. a Documentation bug
          c. me not properly copying/pasting the example :/


Move everything out of "main" and it will work.

-- 
/Jacob Carlborg
Aug 19 2013
parent reply "Craig Dillabaugh" <cdillaba cg.scs.carleton.ca> writes:
On Monday, 19 August 2013 at 18:01:40 UTC, Jacob Carlborg wrote:

 On 2013-08-19 19:57, Craig Dillabaugh wrote:

 When I attempt to compile the following example code from the
 section on UDAs
 at:  http://dlang.org/attribute.html

 void main(string args[]) {
 template Tuple (T...)
 {
          alias T Tuple;
 }

 enum EEE = 7;
  ("hello") struct SSS { }
  (3) {  (4)  EEE  SSS int foo; }

 alias Tuple!(__traits(getAttributes, foo)) TP;

 pragma(msg, TP); // prints tuple(3, 4, 7, (SSS))
 pragma(msg, TP[2]); // prints 7
 }

 I get the following errors:

 UDAs.d(9): Error: basic type expected, not {
 UDAs.d(9): Error: no identifier for declarator int
 UDAs.d(9): Error: semicolon expected, not '{'

 Line 9 is the one starting " (3) ..."

 Is this due to:
         a. a DMD bug (DMD64 D Compiler v2.063.2, Linux)
         b. a Documentation bug
         c. me not properly copying/pasting the example :/


 Move everything out of "main" and it will work.


So I guess it was option (c) after all.

I am still curious though was is wrong using UDAs inside main().
If I have the following code inside main.

      (7) int b;
     pragma(msg, __traits(getAttributes, b) );

or
      ("goodbye") struct D {}
     pragma(msg, __traits(getAttributes, D) );

Then it compiles fine.  But if I make it:

      (7) {  {11} int b; }
     pragma(msg, __traits(getAttributes, b) );

Then I get the same error.

Craig
Aug 19 2013
parent reply "Dicebot" <public dicebot.lv> writes:
On Monday, 19 August 2013 at 18:21:26 UTC, Craig Dillabaugh wrote:

 I am still curious though was is wrong using UDAs inside main().


It is not exactly about UDA - key is different meaning of curly 
brace {} syntax in function bodies and in declaration scopes.

Used in declaration scope {} apply all attributes attached to it 
to every declaration inside:

const
{
     int a;
     double b;
}

static assert (is(typeof(a) == const));

This also applies for UDA's.

In function body it creates new variable scope - variables 
declared inside get destroyed upon leaving the scope and are not 
available outside.

void foo()
{
     {
        int a;
     }
     // a = 42; // error
}

As this usage of {} does not expect any attribute propagation, 
UDA's get rejected too.
Aug 19 2013
parent "Craig Dillabaugh" <cdillaba cg.scs.carleton.ca> writes:
On Monday, 19 August 2013 at 18:28:24 UTC, Dicebot wrote:

 On Monday, 19 August 2013 at 18:21:26 UTC, Craig Dillabaugh 
 wrote:

 I am still curious though was is wrong using UDAs inside 
 main().


 It is not exactly about UDA - key is different meaning of curly 
 brace {} syntax in function bodies and in declaration scopes.

 Used in declaration scope {} apply all attributes attached to 
 it to every declaration inside:

 const
 {
     int a;
     double b;
 }

 static assert (is(typeof(a) == const));

 This also applies for UDA's.

 In function body it creates new variable scope - variables 
 declared inside get destroyed upon leaving the scope and are 
 not available outside.

 void foo()
 {
     {
        int a;
     }
     // a = 42; // error
 }

 As this usage of {} does not expect any attribute propagation, 
 UDA's get rejected too.


Thank you, makes perfect sense.
Aug 19 2013