On 13-05-2012 21:51, Guillaume Chatelet wrote:
Sure enough bitfields is a strange beast and I ran into some subtleties with purity and nothrow.Consider the following code : ------------------------------ struct POD { int a; } int getA(POD o) pure nothrow { return o.a; } POD setA(POD o, int value) pure nothrow { o.a = value; return o; } ------------------------------ It compiles fine. But now with a bitfield : struct POD { mixin(std.bitmanip.bitfields!( int, "a",10, int, "", 22)); } The compiler complains about missing pure and nothrow attributes Error: pure function 'getA' cannot call impure function 'a' Error: o.a is not nothrow Error: function test.getA 'getA' is nothrow yet may throw Error: pure function 'setA' cannot call impure function 'a' Error: o.a is not nothrow Error: function test.setA 'setA' is nothrow yet may throw Which makes sense as the mixin outputs : ------------------------------ @property uint a() const { auto result = (_a_& 1023U)>>0U; return cast(uint) result; } @property void a(uint v){ assert(v>= a_min); assert(v<= a_max); _a_ = cast(typeof(_a_)) ((_a_& ~1023U) | ((cast(typeof(_a_)) v<< 0U)& 1023U)); } enum uint a_min = cast(uint)0U; enum uint a_max = cast(uint)1023U; private uint _a_; ------------------------------ IMHO getters and setters could be nothrow but what about purity ? Looks like it's a bit far-fetched to qualify member methods as pure right ? Yet it makes sense regarding the semantic. What's your take on that ?
I've sent a pull request that fixes this: https://github.com/D-Programming-Language/phobos/pull/583
-- - Alex
