Re: Places a TypeTuple can be used

[monarch_dodra]

On Friday, 16 August 2013 at 05:39:32 UTC, Meta wrote:
On Friday, 16 August 2013 at 04:14:04 UTC, Ali Çehreli wrote:
I know of three places a TypeTuple can be used at:
1) Function parameter list

2) Template parameter list

3) Array literal element list

Are there more?

import std.typetuple;

void foo(int, string, double)
{}

struct S(T, float f)
{}

void main()
{
   // 1) Function parameter list: May not contain types
   foo(TypeTuple!(42, "hello", 1.5));

   // 2) Template parameter list: May contain types
   auto s = S!(TypeTuple!(char, 2.5))();

   // 3) Array elements: Elements must be the same type
   auto a = [ TypeTuple!(1, 2, 3, 4) ];

   // Are there other places that a TypeTuple can be used?
}

Ali

I'm not sure if it should be considered a separate case, but 
there is this:

foreach(type; TypeTuple!(ubyte, uint, ulong))
{
    writeln(type.max);
}

This works for values too btw:

This creates an explicitly unrolled loop, for example.
a = 1;
foreach(type; TypeTuple!(1, 2, 3))
    a *= i;

Or, extracted and simplified from UTF:
private dchar decodeImpl(auto ref S str, ref size_t index)
{
    assert(fst & 0x80);
    ubyte tmp = void;
    dchar d = fst; // upper control bits are masked out later
    fst <<= 1;

    foreach (i; TypeTuple!(1, 2, 3))
    {
        tmp = pstr[i];

        if ((tmp & 0xC0) != 0x80)
            throw invalidUTF();

        d = (d << 6) | (tmp & 0x3F);
        fst <<= 1;

        if (!(fst & 0x80)) // no more bytes
        {
            d &= bitMask[i]; // mask out control bits

            // overlong, could have been encoded with i bytes
            if ((d & ~bitMask[i - 1]) == 0)
                throw invalidUTF();

            // check for surrogates only needed for 3 bytes
            static if (i == 2)
            {
                if (!isValidDchar(d))
                    throw invalidUTF();
            }

            index += i + 1;
            return d;
        }
    }

    throw invalidUTF();
}

Here, notice that the loop is repeated 3 times, but loop number 2 
is statically different from the other loops, by using a "static 
if (i == 2)"