Proposal for SentinelInputRange

[jerro]

> I didn't say can't, I said didn't. llvm handles that case 
> (which does surprise me), dmc, gcc, and vc do not. Furthermore, 
> I'll say "cannot" on this:
>
>             case '|':
>                 p++;
>                 if (*p == '=')
>                 {   p++;
>                     t->value = TOKorass;
>                 }
>                 else if (*p == '|')
>                 {   p++;
>                     t->value = TOKoror;
>                 }
>                 else
>                     t->value = TOKor;
>                 return;

This code is correct without assuming that r is a sentinel range, 
and it is pretty close to your code above:

void foo(R)(ref R r, ref int tvalue)
{
     if(!r.empty)
         switch(r.front)
         {
             case '|':
                 r.popFront();
                 if (!r.empty && r.front == '=')
                 {   r.popFront();
                     tvalue = 1;
                 }
                 else if (!r.empty && r.front == '|')
                 {   r.popFront();
                     tvalue = 2;
                 }
                 else
                     tvalue = 3;
                 return;
             default:
         }
}

If I add this:

struct R
{
     ubyte* p;
     @property front(){ return *p; }
     @property empty(){ return *p == 0; }
     void popFront() { p++; }
}

alias foo!R bar;

ldc2 -O3 -release compiles it to:

    0:  mov    (%rsi),%rax
    3:  cmpb   $0x7c,(%rax)
    6:  jne    3e
    8:  lea    0x1(%rax),%rcx
    c:  mov    %rcx,(%rsi)
    f:  mov    0x1(%rax),%cl
   12:  cmp    $0x7c,%cl
   15:  jne    25
   17:  add    $0x2,%rax
   1b:  mov    %rax,(%rsi)
   1e:  movl   $0x2,(%rdi)
   24:  retq
   25:  cmp    $0x3d,%cl
   28:  jne    38
   2a:  add    $0x2,%rax
   2e:  mov    %rax,(%rsi)
   31:  movl   $0x1,(%rdi)
   37:  retq
   38:  movl   $0x3,(%rdi)
   3e:  retq