[WIP] core.array.staticArray static array litteral: staticArray(1, 2, 3)

src/core/array.d

@@ -0,0 +1,161 @@
+module core.array;
+
+import core.internal.traits : Unqual, CommonType;
+
+debug import std.stdio;
+
+// @nogc: https://issues.dlang.org/show_bug.cgi?id=18439
+nothrow @safe pure:
+
+/++
+Returns a static array constructed from `a`. The type of elements can be
+specified implicitly (`int[2] a = staticArray(1,2);`) or explicitly
+(`float[2] a = staticArray!float(1,2)`).
+D20180214T203015: The result is an rvalue, therefore uses like
+`foo(staticArray(1, 2, 3)` may be inefficient because of the copies.
++/
+pragma(inline, true) U[T.length] staticArray(U = CommonType!T, T...)(T a) @nogc
+{
+    return [a];
+}
+
+// D20180214T185602: Workaround https://issues.dlang.org/show_bug.cgi?id=16779 (make alias to staticArray once fixed)
+pragma(inline, true) U[T.length] staticArrayCast(U, T...)(T a) @nogc
+{
+    enum n = T.length;
+    U[n] ret = void;
+    static foreach (i; 0 .. n)
+        cast(Unqual!U)(ret[i]) = cast(U)(a[i]);
+    return ret;
+}
+
+///
+unittest
+{
+    {
+        auto a = staticArray(1, 2, 3);
+        assert(is(typeof(a) == int[3]));
+        assert(a == [1, 2, 3]);
+    }
+    {
+        auto a = staticArray(1, 2.0);
+        assert(is(typeof(a) == double[2]));
+        assert(a == [1, 2.0]);
+    }
+    assert(!__traits(compiles, staticArray(1, "")));
+    assert(is(typeof(staticArray()) == void[0]));
+
+    {
+        auto a = staticArray!float(1, 2);
+        assert(is(typeof(a) == float[2]));
+        assert(a == [1, 2]);
+
+    }
+    {
+        // see D20180214T185602
+        // auto a = staticArray!byte(1, 2);
+        auto a = staticArrayCast!byte(1, 2);
+        assert(is(typeof(a) == byte[2]));
+        assert(a == [1, 2]);
+    }
+    {
+        auto a = staticArrayCast!byte(1, 129);
+        assert(a == [1, -127]);
+    }
+
+    assert(is(typeof(staticArray([1])) == int[][1]));
+
+    // NOTE: correctly issues a deprecation
+    // int[] a2 = staticArray(1,2);
+}
+
+/++
+Returns a static array constructed from `arr`. The type of elements can be
+specified implicitly (`int[2] a = [1,2].asStatic;`) or explicitly
+(`float[2] a = [1,2].asStatic!float`).
+See also D20180214T203015.
++/
+pragma(inline, true) T[n] asStatic(T, size_t n)(auto ref T[n] arr) @nogc
+{
+    return arr;
+}
+
+//U[n] asStatic(U, T, size_t n)(auto ref T[n] arr) @nogc if (!is(U == T) && is(T : U))
+U[n] asStatic(U, T, size_t n)(auto ref T[n] arr) @nogc if (!is(U == T))
+{
+    U[n] ret = void;
+    static foreach (i; 0 .. n)
+        cast(Unqual!U)(ret[i]) = arr[i];
+    return ret;
+}
+
+/// ditto
+auto asStatic(U = typeof(arr[0]), alias arr)() @nogc
+{
+    enum n = arr.length;
+    U[n] ret = void;
+    static foreach (i; 0 .. n)
+        cast(Unqual!U)(ret[i]) = arr[i];
+    return ret;
+}
+
+/// ditto
+auto asStatic(alias arr)() @nogc
+{
+    enum n = arr.length;
+    alias U = typeof(arr[0]);
+    U[n] ret = void;
+    static foreach (i; 0 .. n)
+        cast(Unqual!U)(ret[i]) = arr[i];
+    return ret;
+}
+
+///
+unittest
+{
+    {
+        auto a = [1, 2, 3].asStatic;
+        assert(is(typeof(a) == int[3]));
+        assert(a == [1, 2, 3]);
+    }
+
+    @nogc void checkNogc()
+    {
+        auto a = [1, 2, 3].asStatic;
+        assert(a == [1, 2, 3]);
+    }
+
+    {
+        auto a = [1, 2, 3].asStatic!double;
+    }
+
+    {
+        auto a = [1, 2, 3].asStatic!int;
+        // https://issues.dlang.org/show_bug.cgi?id=16779
+        //auto a2 = [1, 2, 3].asStatic!byte;
+        //auto a3 = [1, 2, 3].asStatic!ubyte;
+    }
+    {
+        auto a1 = [1, 2, 3].asStatic!(const(int));
+        const(int)[3] a2 = [1, 2, 3].asStatic;
+        auto a3 = [1, 2, 3].asStatic!(const(double));
+    }
+
+    {
+        import std.range;
+
+        enum a = asStatic!(double, 2.iota);
+        assert(is(typeof(a) == double[2]));
+        assert(a == [0, 1]);
+    }
+    {
+        import std.range;
+
+        enum a = asStatic!(2.iota);
+        assert(is(typeof(a) == int[2]));
+        assert(a == [0, 1]);
+    }
+
+    // NOTE: correctly issues a deprecation
+    //int[] a2 = [1,2].asStatic;
+}

src/core/internal/traits.d

@@ -230,3 +230,30 @@ template staticMap(alias F, T...)
                 staticMap!(F, T[$/2 ..  $ ]));
     }
 }
+
+// std.traits.CommonType
+template CommonType(T...)
+{
+    static if (!T.length)
+    {
+        alias CommonType = void;
+    }
+    else static if (T.length == 1)
+    {
+        static if (is(typeof(T[0])))
+        {
+            alias CommonType = typeof(T[0]);
+        }
+        else
+        {
+            alias CommonType = T[0];
+        }
+    }
+    else static if (is(typeof(true ? T[0].init : T[1].init) U))
+    {
+        alias CommonType = CommonType!(U, T[2 .. $]);
+    }
+    else
+        alias CommonType = void;
+}
+