On Tuesday, 12 December 2017 at 09:48:09 UTC, Jonathan M Davis
wrote:
On Tuesday, December 12, 2017 07:33:47 Ivan Trombley via
Digitalmars-d-learn wrote:
Is there some way that I can make this array immutable?
static float[256] ga = void;
static foreach (i; 0 .. 256)
ga[i] = (i / 255.0f) ^^ (1 / 2.2f);
If you want anything to be immutable, you either have to
initialize it directly or give it a value in a static
constructor (and the static constructor solution won't work for
local variables). So, you'd need to do something like
static immutable float[256] ga = someFuncThatGeneratesGA();
If the function is pure, and there's no way that the return
value was passed to the function, then its return value can be
assigned to something of any mutability, since the compiler
knows that there are no other references to it, and it can
implicitly cast it, or if the type is a value type (as in this
case), then you just get a copy, and mutability isn't an issue.
Alternatively to using a pure function, you can use
std.exception.assumeUnique to cast to immutable, but that
relies on you being sure that there are no other references to
the data, and it may not work at compile-time, since casting is
a lot more restrictive during CTFE. So, in general, using a
pure function is preferable to assumeUnique.
- Jonathan M Davis
Ah, it doesn't work. I get this error using the ^^ operator:
/usr/include/dmd/phobos/std/math.d(5724,27): Error: cannot
convert &real to ubyte* at compile time
/usr/include/dmd/phobos/std/math.d(6629,24): called from
here: signbit(x)
/usr/include/dmd/phobos/std/math.d(6756,16): called from
here: impl(cast(real)x, cast(real)y)
:(
