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Re: void

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  Re: void Martin Gregorie <martin@address-in-sig.invalid> - 2016-07-16 22:49 +0000
    Re: void Steven Simpson <ss@my.domain.invalid> - 2016-07-17 09:21 +0100
      Re: void Martin Gregorie <martin@address-in-sig.invalid> - 2016-07-17 18:36 +0000
        Re: void Steven Simpson <ss@my.domain.invalid> - 2016-07-17 20:17 +0100
          Re: void Martin Gregorie <martin@address-in-sig.invalid> - 2016-07-17 22:15 +0000
            Re: void Martin Gregorie <martin@address-in-sig.invalid> - 2016-07-17 22:26 +0000

#34929 — Re: void

On Sat, 16 Jul 2016 22:20:20 +0000, Stefan Ram wrote:

> On several occassions I have observed that the compiler, javac,
>   has it's own vocabulary. For example, it uses words like »context«
>   or »symbol« that might not be used this way in the JLS.
> 
>   Another example I encountered today:
> 
>   The JLS does not seem to think of »void« as a »type«. It says:
> 
> 8.4.5 Method Result
> 
> The result of a method declaration either declares the type of value
> that the method returns (the return type), or uses the keyword void to
> indicate that the method does not return a value.
> 
>   (end of quotation).
> 
>   But for the compiler, it seems to be a »type«:
> 
> Main.java:3: error: 'void' type not allowed here
> java.lang.System.out.println( java.lang.System.out.println() ); }}
>   
My guess is that the compiler does that because it has a single error 
message template, something like

%s:%d: error '%s' type not allowed here

so the least stupid thing it can use to describe the absence of arguments 
when they're expected is the work void which, in Java, always means an 
absence of an argument or return value.

This is unlike C, where a function declared as "void free(void ptr)" 
means that free() takes an untyped pointer and returns an untyped pointer 
value. BUT note the void as a return value is ambiguous in C because it 
can also mean that nothing is returned by a function.


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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#34936

On 16/07/16 23:49, Martin Gregorie wrote:
> This is unlike C, where a function declared as "void free(void ptr)"
> means that free() takes an untyped pointer and returns an untyped pointer
> value.

Hmm?  You mean "void *free(void *)", surely?

> BUT note the void as a return value is ambiguous in C because it
> can also mean that nothing is returned by a function.

There's no ambiguity; a void return type only ever means that nothing is 
returned.  void* is a different type, related to void mnemonically at best.


-- 
ss at comp dot lancs dot ac dot uk

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#34940

On Sun, 17 Jul 2016 09:21:05 +0100, Steven Simpson wrote:

> On 16/07/16 23:49, Martin Gregorie wrote:
>> This is unlike C, where a function declared as "void free(void ptr)"
>> means that free() takes an untyped pointer and returns an untyped
>> pointer value.
> 
> Hmm?  You mean "void *free(void *)", surely?
>

The manpage says "void free(void *ptr)".


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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#34944

On 17/07/16 19:36, Martin Gregorie wrote:
> On Sun, 17 Jul 2016 09:21:05 +0100, Steven Simpson wrote:
>
>> On 16/07/16 23:49, Martin Gregorie wrote:
>>> This is unlike C, where a function declared as "void free(void ptr)"
>>> means that free() takes an untyped pointer and returns an untyped
>>> pointer value.
>> Hmm?  You mean "void *free(void *)", surely?
>>
> The manpage says "void free(void *ptr)".

I was talking about the function you described as taking and returning 
an "untyped pointer (value)".

-- 
ss at comp dot lancs dot ac dot uk

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#34945

On Sun, 17 Jul 2016 20:17:58 +0100, Steven Simpson wrote:

> On 17/07/16 19:36, Martin Gregorie wrote:
>> On Sun, 17 Jul 2016 09:21:05 +0100, Steven Simpson wrote:
>>
>>> On 16/07/16 23:49, Martin Gregorie wrote:
>>>> This is unlike C, where a function declared as "void free(void ptr)"
>>>> means that free() takes an untyped pointer and returns an untyped
>>>> pointer value.
>>> Hmm?  You mean "void *free(void *)", surely?
>>>
>> The manpage says "void free(void *ptr)".
> 
> I was talking about the function you described as taking and returning
> an "untyped pointer (value)".

Which I thought free() did.


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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#34946

On Sun, 17 Jul 2016 22:15:02 +0000, Martin Gregorie wrote:

> On Sun, 17 Jul 2016 20:17:58 +0100, Steven Simpson wrote:
> 
>> On 17/07/16 19:36, Martin Gregorie wrote:
>>> On Sun, 17 Jul 2016 09:21:05 +0100, Steven Simpson wrote:
>>>
>>>> On 16/07/16 23:49, Martin Gregorie wrote:
>>>>> This is unlike C, where a function declared as "void free(void ptr)"
>>>>> means that free() takes an untyped pointer and returns an untyped
>>>>> pointer value.
>>>> Hmm?  You mean "void *free(void *)", surely?
>>>>
>>> The manpage says "void free(void *ptr)".
>> 
>> I was talking about the function you described as taking and returning
>> an "untyped pointer (value)".
> 
> Which I thought free() did.

But was wrong.


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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