The following compiles fine:
immutable char[5] array = x"01 02 03 04 05";

The following doesn't:
immutable ubyte[5] array = x"01 02 03 04 05";

which makes sense, but neither does:
immutable ubyte[5] array = cast(immutable ubyte []) x"01 02 03 04 05";

playground.d(1): Error: cannot implicitly convert expression ("\x01\x02\x03\x04\x05") of type immutable(ubyte[]) to immutable(ubyte[5])

Just to make sure we're clear, the following (no op) cast still compiles:
immutable char[5] array = cast(immutable char []) x"01 02 03 04 05";


To summarize: An immutable(char[]) is a valid initializer for an immutable(char[5]), but an immutable(ubyte[]) is not a valid initializer for an immutable(ubyte[5]).

Why?

Just in case anyone is going to claim that the cast to another type destroys the compiler's understanding of what this is, the following works:

immutable char[5] array = cast(immutable (char[]))(cast(immutable ubyte[]) x"0102030405");

All examples with dmd 2.072.1

Shachar

On Monday, 12 December 2016 at 06:43:52 UTC, Shachar Shemesh wrote:
> The following compiles fine:
> immutable char[5] array = x"01 02 03 04 05";
>
> [...]

This doesn't seem like a bug:
> immutable ubyte[5] array = x"01 02 03 04 05";

This however does:
> immutable ubyte[5] array = cast(immutable ubyte []) x"01 02 03 04 05";

There's a workaround for this though.

immutable ubyte[5] array = cast(immutable(ubyte[5]))x"01 02 03 04 05";