stdio line-streaming revisited

[Andrei Alexandrescu (See Website For Email)]

Sean Kelly wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> kris wrote:
>>> Sean Kelly wrote:
>>> [snip]
>>>> I must be missing something.  Why is the following not acceptable?
>>>>
>>>>     import tango.io.Console;
>>>>
>>>>     void main()
>>>>     {
>>>>         char[] name;
>>>>         Cout( "Please enter your name: " ).flush;
>>>>         Cin.nextLine( name );
>>>>         Cout( "Hello, " )( name )( "!" );
>>>>     }
>>>
>>>
>>> There used to be a tango/example like this variation:
>>>
>>>     import tango.io.Console;
>>>
>>>     void main()
>>>     {
>>>         Cout ("Please enter your name: ").flush;
>>>         Cout ("Hello, ") (Cin.get);
>>>     }
>>
>> Ah, also, the last line is translated into:
>>
>> Cout.opCall("Hello, ").opCall(Cin.get);
>>
>> D does not specify evaluation order, so the code might end up printing 
>> "Hello, " before reading the standard input.
> 
> We discussed this a long time ago and came to the conclusion that while 
> the D spec does not guarantee evaluation order for this scenario, it 
> seems impossible for it to be anything other than left to right because 
> the chained calls rely on the return value from previous calls.  If this 
> is untrue then I'd love to know the reasoning.  Perhaps an aggressive 
> inlining mechanism could violate this?

Frits has provided the exact explanation. What you say would be true in 
the case:

Cout("Hello, ", Cin.get);

Then it's clear that Cout can't possibly be called before Cin.get 
returned. So variadics are the best solution in this case too :o).


Andrei