[chuck-users] "pure"

[Robert Poor]

I need to know: How did Tom find out about the "pure" keyword in the  
first place?  By consulting the "authoritative documentation" [i.e.  
chuck_type.cpp :)]?  Is reading the source code the only way to learn  
about these things? (Ditto for "interface"...)

As an aside, I appreciate the value of "programming by contract"  
constructs.

- Rob

On 9 May 2009, at 13:48, Andrew Turley wrote:

> If I didn't know any better (and I don't) I would guess that calling a
> method "pure" is a way of indicating that any class that implements X
> must provide a function called "doit()", but that X will not provide a
> default implementation of that method. It forces the child class to
> provide the implementation.
>
> If you wrote:
>
> class X {
>   fun void doit() {};
> }
>
> and then created a class Y that extends class X, Y would not have to
> provide an implementation of "doit()". Take a look at pure virtual
> classe in C++, interfaces in Java, or abstract classes in general.
>
> One of the uses for pure function is to help with "programming by
> contract" where other methods and functions will accept objects that
> are guaranteed to provide *some* implementation of a method, without
> making any claims about what that method will do.
>
> andy
>
> On Sat, May 9, 2009 at 12:38 PM, Tom Lieber <lieber at princeton.edu>  
> wrote:
>> class X {
>>    fun void doit();
>> }
>>
>> [Untitled]:line(2): function declaration must contain code...
>> [Untitled]:line(2): (unless in interface, or is declared 'pure')
>> [Untitled]:line(2): ...at function 'doit'
>>
>> interface X {
>>    fun void doit();
>> }
>>
>> [Untitled]:line(2): function declaration must contain code...
>> [Untitled]:line(2): (unless in interface, or is declared 'pure')
>> [Untitled]:line(2): ...at function 'doit'
>>
>> class X {
>>    fun pure void doit();
>> }
>>
>> [chuck](VM): sporking incoming shred: 1 (Untitled)...
>>
>> Does anybody use "pure" or know what it does? The last example seems
>> to be equivalent to saying "fun void doit() { }".
>>
>> --
>> Tom Lieber
>> http://AllTom.com/
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