I'd like to check whether a variable is initialized or not. And I'd also like to uninitialize a variable that is already initialized. Thanks!

int x = void;

if (x == void)
{
    writeln("x not initialized");
}
else
{
    // OK, use x
}

// Uninitialize x
x = void;

On 9/5/20 11:42 PM, N.S. wrote:
> I'd like to check whether a variable is initialized or not. And I'd also like to uninitialize a variable that is already initialized. Thanks!
> 
> int x = void;
> 
> if (x == void)

There isn't a way to check this.

> {
>      writeln("x not initialized");
> }
> else
> {
>      // OK, use x
> }
> 
> // Uninitialize x
> x = void;
> 

When you set the initial value of x to void, it means "don't do anything, let whatever data is already on the stack be the value of x".

So "uninitialize" doesn't really mean anything. It would technically mean "do nothing".

-Steve

On Sunday, 6 September 2020 at 03:56:51 UTC, Steven Schveighoffer wrote:
> On 9/5/20 11:42 PM, N.S. wrote:
>> I'd like to check whether a variable is initialized or not. And I'd also like to uninitialize a variable that is already initialized. Thanks!
>> 
>> int x = void;
>> 
>> if (x == void)
>
> There isn't a way to check this.
>
>> {
>>      writeln("x not initialized");
>> }
>> else
>> {
>>      // OK, use x
>> }
>> 
>> // Uninitialize x
>> x = void;
>> 
>
> When you set the initial value of x to void, it means "don't do anything, let whatever data is already on the stack be the value of x".
>
> So "uninitialize" doesn't really mean anything. It would technically mean "do nothing".
>
> -Steve

Do I have to create additional variable bool x_is_valid? Problem is I got many variables. Thanks.

On Sunday, 6 September 2020 at 03:42:36 UTC, N.S. wrote:
> I'd like to check whether a variable is initialized or not. And I'd also like to uninitialize a variable that is already initialized. Thanks!
>
> int x = void;
>
> if (x == void)
> {
>     writeln("x not initialized");
> }
> else
> {
>     // OK, use x
> }
>
> // Uninitialize x
> x = void;

You might consider Nullable from std.typecons; however, if you're avoiding implicit initialization for performance reasons, then this solution might not be applicable.

import std.stdio: writeln;
import std.typecons: Nullable;

Nullable!int x;

if (x.isNull)
{
	writeln("x not 'initialized'");
}
else
{
	// OK, use x
}

// 'Uninitialize' x
x.nullify();

On Sunday, 6 September 2020 at 05:06:26 UTC, starcanopy wrote:
> On Sunday, 6 September 2020 at 03:42:36 UTC, N.S. wrote:
>> I'd like to check whether a variable is initialized or not. And I'd also like to uninitialize a variable that is already initialized. Thanks!
>>
>> int x = void;
>>
>> if (x == void)
>> {
>>     writeln("x not initialized");
>> }
>> else
>> {
>>     // OK, use x
>> }
>>
>> // Uninitialize x
>> x = void;
>
> You might consider Nullable from std.typecons; however, if you're avoiding implicit initialization for performance reasons, then this solution might not be applicable.
>
> import std.stdio: writeln;
> import std.typecons: Nullable;
>
> Nullable!int x;
>
> if (x.isNull)
> {
> 	writeln("x not 'initialized'");
> }
> else
> {
> 	// OK, use x
> }
>
> // 'Uninitialize' x
> x.nullify();

Perfect, thanks!