Re: IFTI with value / template value parameter shadowing

2014-02-24 Thread Mathias LANG 

On Sunday, 23 February 2014 at 11:49:26 UTC, Marc Schütz wrote:
There's no IFTI here. IFTI is about inferring a template 
argument (= type) from the type of a function argument. Your 
template argument is a value, not a type, so there's nothing to 
infer.


There is the value. In IFTI_Type, the compiler understands that 
the 'T' in the parameter list is the same as the 'T' in the 
TemplateArgumentList.


For example this code compiles (from bug #4986):
-
struct Foo(int n, int m) {
   void bar(int m2)(Foo!(m2, n) arg) {}
}

void main( )( ) {
   Foo!(3,2) f;
   Foo!(3,3) g;
   f.bar(g);
}
-
So the compiler can deduce a value argument from a type, but not 
from a value known at compile time.



Not sure what you want to achieve. Do you want IFTI_Value(6) to 
be instantiated as IFTI_Value!6(6)? In this case, just leave 
the runtime parameter out:


Yeah that works, and actually I agree that passing a value both 
in the parameters and template argument seems silly / odd at 
first sight. But there can be valid reasons to do so. I came 
accross this example while trying to shift a runtime argument to 
compile time while keeping source-level compatibility in a 
library.



In addition it looks like template parameter are not 
considered while looking if a symbol with shadow another one. 
I didn't find anything on the bugtracker but 
(this)[https://d.puremagic.com/issues/show_bug.cgi?id=6980], 
but it's only related.


I believe it works exactly as intended. The short form for 
template functions is just syntactic sugar for:


template IFTI_Value(int n) {
int IFTI_Value(int n) { return n; }
}

This means that the function (runtime) parameter n is declared 
in the inner scope, and is thus expected to shadow the template 
parameter n in the outer scope.


I have to give it a second read but IIRC the TDPL was pretty much 
saying that shadowing is not legal in D.

Re: IFTI with value / template value parameter shadowing

2014-02-23 Thread Marc Schütz 

On Sunday, 23 February 2014 at 02:46:24 UTC, Mathias LANG wrote:

int IFTI_Value(int n)(int n)  { return n; }
...
So from the commented call to IFTI_Value, I guessed that IFTI 
is not working for values. Is that intended behavior, or a bug ?


There's no IFTI here. IFTI is about inferring a template argument 
(= type) from the type of a function argument. Your template 
argument is a value, not a type, so there's nothing to infer.


Not sure what you want to achieve. Do you want IFTI_Value(6) to 
be instantiated as IFTI_Value!6(6)? In this case, just leave the 
runtime parameter out:


int IFTI_Value(int n)() { return n; }

Of course, you will have to use the ! syntax then:

assert(IFTI_Value!6() == 6);

In addition it looks like template parameter are not considered 
while looking if a symbol with shadow another one. I didn't 
find anything on the bugtracker but 
(this)[https://d.puremagic.com/issues/show_bug.cgi?id=6980], 
but it's only related.


I believe it works exactly as intended. The short form for 
template functions is just syntactic sugar for:


template IFTI_Value(int n) {
int IFTI_Value(int n) { return n; }
}

This means that the function (runtime) parameter n is declared in 
the inner scope, and is thus expected to shadow the template 
parameter n in the outer scope.

IFTI with value / template value parameter shadowing

2014-02-22 Thread Mathias LANG 

Hi everyone,
I recently end up with the following code:


import std.stdio;

T IFTI_Type(T)(T value)   { return value; }

int IFTI_Value(int n)(int n)  { return n; }

int Shadowing_FTW(int n)()
{
   writeln(n);
   int n = 42; // Will print 6
   return n;
}


voidmain()
{
writeln(IFTI_Type(5));// Will print 5
writeln(Shadowing_FTW!6());   // Will print 42
// This doesn't compile
//writeln(IFTI_Value(5));
writeln(IFTI_Value!5(8)); // Will print 8
}


This will print:
5
6
42
8

So from the commented call to IFTI_Value, I guessed that IFTI is 
not working for values. Is that intended behavior, or a bug ?
In addition it looks like template parameter are not considered 
while looking if a symbol with shadow another one. I didn't find 
anything on the bugtracker but 
(this)[https://d.puremagic.com/issues/show_bug.cgi?id=6980], but 
it's only related.