Suggestion: adding stubs to function definition

[claudio fanelli]

I am not an expert in languages ( I don't know neither english, it is not  
my language :-) ),
but I think that adding a "stub" section in function definition can make D  
better.

Consider this example:

///this function returns the integer part of the square root of its input
int isqrt(int x)
in{
	assert(x0=>0);
}
out(y) {
	assert( y*y <= x );
	assert( (y+1)*(y+1) >= x);
}
stub{
	if(x<4) return 1;
	if(x<9) return 2;
       if(x<16) return 3;
}
body {
   //TODO
}

the stub section is optional, and if there is a stub section, the body  
section is optional.
Probably there is the need for a fixed structure in a stub section, maybe  
allowing only
if-statements, return and accessing simple variables (calling a function,  
or using loops must be disallowed ).
The stub section can be used for:

1) prototyping: if writing the function body is complex,it is possible  
initially to  write a simple stub

2) debugging: when there are both a stub section and a body section, it is  
possible the compare the results returned by both at compile time (in  
simple cases).

3) optimization: the information in the stub section can be used for  
optimize the code generated.
For example if somewhere there is the code

    z=30/isqrt(7);

the compiler can convert this code to z=30/2; and then to z=15;

I am aware that stubs do not add new functions to D, and also that they  
can add complexity to the compiler, because I think that it is not easy to  
extract the information for 2) and 3) in the general case (for example if  
the input parameters of the function are objects or complex types), but  
there are cases in which adding the functionality 2 and 3 is trivial.
Greetings.

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