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digitalmars.D.learn - Is variable void?

reply John Chapman <johnch_atms hotmail.com> writes:
Is there any way of determining whether a variable has been 
initialized or not? For example, if something is declared like 
this:

   int x = void;

can I check if it's void before I use it, say, in a function it's 
been passed to?
Nov 25 2017
next sibling parent rikki cattermole <rikki cattermole.co.nz> writes:
On 25/11/2017 3:34 PM, John Chapman wrote:

 Is there any way of determining whether a variable has been initialized 
 or not? For example, if something is declared like this:
 
    int x = void;
 
 can I check if it's void before I use it, say, in a function it's been 
 passed to?


`` = void;`` isn't null.

Don't treat it as such. It is a low level detail where you _will_ 
initialize it, just in a smarter way.

There is no conditions tied directly to it.
Nov 25 2017
prev sibling next sibling parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Saturday, 25 November 2017 at 15:34:21 UTC, John Chapman wrote:

 Is there any way of determining whether a variable has been 
 initialized or not? For example, if something is declared like 
 this:


nope. It'd be indistinguishable from the user just happening to 
initialize it to some random value.
Nov 25 2017
parent John Chapman <johnch_atms hotmail.com> writes:
On Saturday, 25 November 2017 at 15:38:15 UTC, Adam D. Ruppe 
wrote:

 nope. It'd be indistinguishable from the user just happening to 
 initialize it to some random value.


Thanks. I'll got with .init instead.
Nov 25 2017
prev sibling next sibling parent crimaniak <crimaniak gmail.com> writes:
On Saturday, 25 November 2017 at 15:34:21 UTC, John Chapman wrote:

 Is there any way of determining whether a variable has been 
 initialized or not? For example, if something is declared like 
 this:

   int x = void;

 can I check if it's void before I use it, say, in a function 
 it's been passed to?


  You can use Nullable!int
Nov 26 2017
prev sibling parent reply codephantom <me noyb.com> writes:
On Saturday, 25 November 2017 at 15:34:21 UTC, John Chapman wrote:

 Is there any way of determining whether a variable has been 
 initialized or not? For example, if something is declared like 
 this:

   int x = void;

 can I check if it's void before I use it, say, in a function 
 it's been passed to?


// ----------------------------------

module test;

import std.stdio;
import std.typecons; // see: 
https://dlang.org/phobos/std_typecons.html#Nullable

void main()
{
     Nullable!int x;  // requires: import std.typecons
     assert(x.isNull);
     writeln("x is ", x);

     x = 1;
     assert(!x.isNull);
     writeln("x is ", x);

     x.nullify(); //  	Forces x back to a null state.
     assert(x.isNull);
     writeln("x is ", x);

}
// ----------------------------------
Nov 26 2017
parent reply bauss <jj_1337 live.dk> writes:
On Monday, 27 November 2017 at 02:12:40 UTC, codephantom wrote:

 On Saturday, 25 November 2017 at 15:34:21 UTC, John Chapman 
 wrote:

 Is there any way of determining whether a variable has been 
 initialized or not? For example, if something is declared like 
 this:

   int x = void;

 can I check if it's void before I use it, say, in a function 
 it's been passed to?


 // ----------------------------------

 module test;

 import std.stdio;
 import std.typecons; // see: 
 https://dlang.org/phobos/std_typecons.html#Nullable

 void main()
 {
     Nullable!int x;  // requires: import std.typecons
     assert(x.isNull);
     writeln("x is ", x);

     x = 1;
     assert(!x.isNull);
     writeln("x is ", x);

     x.nullify(); //  	Forces x back to a null state.
     assert(x.isNull);
     writeln("x is ", x);

 }
 // ----------------------------------


null != void
Nov 27 2017
next sibling parent codephantom <me noyb.com> writes:
On Tuesday, 28 November 2017 at 05:10:39 UTC, bauss wrote:

 null != void


"initialized or not?" != void
Nov 27 2017
prev sibling parent codephantom <me noyb.com> writes:
On Tuesday, 28 November 2017 at 05:10:39 UTC, bauss wrote:

 null != void



also...void is a completely useless concept for initialisation.

what can you determine about the nothingness of void? ... nothing.


writeln(typeof(void).stringof); // ?? what do I know now? nothing.

vs

Nullable!int x;
writeln(typeof(x).stringof); // Nullable!int .. now I know 
something.
Nov 27 2017