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digitalmars.D.learn - How should this be done? (1.0)

reply Michael Coupland <mcoupland gmail.com> writes:
The following doesn't work because I'm trying to use a template mixin 
like a string constant mixin, and you can't actually do calculations in 
a template like this. (You get "no identifier for declarator" errors on 
the assignment lines.) What is the Proper D Way to do this? (I'd rather 
not use a function that returns a struct; in C/C++ one would probably 
use a macro.) I considered a heredoc string and doing a proper textual 
mixin, but that feels like overkill...

	Michael

-----------------------------------------------

template CommonCalculations()
{
     bool commonBool1;
     bool commonBool2;
	
     {
         int LocalVal = SomeFn();
         commonBool1 = SomeOtherFunc();
	commonBool2 = AThirdFunction(LocalVal,commonBool1);
     }
};

// (...)

{
	mixin CommonCalculations!();
	// do stuff here with commonBool1 and commonBool2
}
Feb 04 2008
next sibling parent reply Derek Parnell <derek nomail.afraid.org> writes:
On Mon, 04 Feb 2008 21:49:50 -0800, Michael Coupland wrote:

 I considered a heredoc string and doing a proper textual 
 mixin, but that feels like overkill...

What is 'overkill' about this ... const char[] CommonCalculations = r" bool commonBool1; bool commonBool2; { int LocalVal = SomeFn(); commonBool1 = SomeOtherFunc(); commonBool2 = AThirdFunction(LocalVal,commonBool1); } " . . . { mixin (CommonCalculations); // do stuff here with commonBool1 and commonBool2 } -- Derek (skype: derek.j.parnell) Melbourne, Australia 5/02/2008 6:10:32 PM
Feb 04 2008
parent reply Michael Coupland <mcoupland gmail.com> writes:
Correct me if I'm wrong, but I think it has several of the same problems 
that a normal macro has. Compiler errors in the heredoc string will be 
reported on the wrong line (presumably debuggers would have similar 
problems) and if you want to parameterize your mixin you run the risk of 
textual duplication. There's also the annoyance that text editors may 
fail to properly format the text (having an editor that doesn't 
recognize my heredoc syntax is helpful in this case.)

Derek Parnell wrote:
 On Mon, 04 Feb 2008 21:49:50 -0800, Michael Coupland wrote:
 
 I considered a heredoc string and doing a proper textual 
 mixin, but that feels like overkill...

What is 'overkill' about this ... const char[] CommonCalculations = r" bool commonBool1; bool commonBool2; { int LocalVal = SomeFn(); commonBool1 = SomeOtherFunc(); commonBool2 = AThirdFunction(LocalVal,commonBool1); } " . . . { mixin (CommonCalculations); // do stuff here with commonBool1 and commonBool2 }

Feb 05 2008
parent Derek Parnell <derek nomail.afraid.org> writes:
On Tue, 05 Feb 2008 21:54:28 -0800, Michael Coupland wrote:

 Correct me if I'm wrong, but I think it has several of the same problems 
 that a normal macro has. 

I see what you're saying. It could be that the future AST macros can help us with this sort of stuff. However, it appears that you'd like to define a named fragment of code that includes arbitrary declarations and executable statements, force that fragment to be in-lined in one or more places (with possibly parameterized textual replacement?), and have any error messages refer to line numbers in the fragment's definition rather than, or as well as, its instantiation location. Example syntax (not wedded to this of course). macro CommonCalculation(alias b1 = defBool1, alias b2 = defBool2) { bool b1; bool b2; void calculate() { int LocalVal = SomeFn(); b1 = SomeOtherFunc(); b2 = AThirdFunction(LocalVal,b1); } } ... { CommonCalculation(commonBool1, commonBool2); // do stuff here with commonBool1 and commonBool2 } ... { CommonCalculation(); // do stuff here with defBool1 and defBool2 } With messages like ... test.d(231): Function 'someFn' not defined. Referenced in macro 'CommonCalculation'(line 48). test.d(493): Function 'someFn' not defined. Referenced in macro 'CommonCalculation'(line 48). -- Derek (skype: derek.j.parnell) Melbourne, Australia 6/02/2008 6:01:14 PM
Feb 05 2008
prev sibling parent Christian Kamm <kamm.incasoftware shift-at-left-and-remove-this.de> writes:
What about the old fashioned way:

struct CommonCalculation
{
    bool commonBool1;
    bool commonBool2;
        
    void calculate()
    {
        int LocalVal = SomeFn();
        commonBool1 = SomeOtherFunc();
        commonBool2 = AThirdFunction(LocalVal,commonBool1);
    }
}


{
    CommonCalculation calc;
    calc.calculate();
    // do stuff here with calc.commonBool1 and calc.commonBool2
}

You could also make the calculate method a static opCall(), which would
reduce the invocation to the line

CommonCalculation calc = CommonCalculation();

But imho that's not much shorter and less obvious.

Christian Kamm
Feb 05 2008