http://d.puremagic.com/issues/show_bug.cgi?id=8995

           Summary: `is(<Type> <Identifier> == function)` creates tuple
                    with parameter storage classes
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: verylonglogin.reg@gmail.com


--- Comment #0 from Denis Shelomovskij <verylonglogin.reg@gmail.com> 2012-11-11 10:28:55 MSK ---
Function parameter types tuple retrieved with `IsExpression` contains parameter storage classes unless indexed (slicing remains storage classes).

It is not documented that typetuple can contain parameter storage classes so it may lead to unexpected behavior and looks inconsistent because `is(typetuple1 == typetuple2)` is `true` for tuples with different storage classes.
---
template TypeTuple(T...)
{ alias T TypeTuple; }

template t(alias func)
{
    static if (is(typeof(func) Args == function))
    {
        static assert(is(Args == TypeTuple!(int, int, int, int))); // passes

        pragma(msg, "Args: ", Args); // (int, ref int, out int, auto int)
        pragma(msg, "Args[1..2]: ", Args[1..2]); // (ref int)
        pragma(msg, "Args[1]: ", Args[1]);       // int

        void g1(Args[0 .. 3]) { } // void(int, ref int, out int)
        pragma(msg, "typeof(g1): ", typeof(g1));

        void g2(Args[3]) { } // void(int)
        pragma(msg, "typeof(g2): ", typeof(g2));

        void g3(Args[3 .. 4]) { } // void(auto ref int), error, line 20
    }
    else
        static assert(0);

}

void f(T)(int, ref int, out int, auto ref T)
{
    alias t!f tf;
}


void main()
{
    int i;
    f(0, i, i, 0);
}
---

Compiler output:
---
Args: (int, ref int, out int, auto int)
Args[1..2]: (ref int)
Args[1]: int
typeof(g1): void(int, ref int, out int)
typeof(g2): void(int)
main.d(20): Error: auto can only be used for template function parameters
main.d(29): Error: template instance main.t!(f) error instantiating
main.d(36):        instantiated from here: f!(int)
main.d(36): Error: template instance main.f!(int) error instantiating
---

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--- Comment #1 from Denis Shelomovskij <verylonglogin.reg@gmail.com> 2012-11-11 10:34:15 MSK ---
Workaround to remove storage classes:
---
import std.typetuple;

template DeStorage(T) { alias T DeStorage; }
alias staticMap!(DeStorage, ArgsWithStorageClasses) Args;
---

Note, it it's not documented, that `staticMap` will use indexing (`A[x]`) instead of slicing (`A[x .. x+1]`) and in latter case this workaround will not work so you have to copy/paste `staticMap` with current behavior to you code.

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