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digitalmars.D.learn - 2.067 Beta: Behavior of enum and ref changed

reply "Andre" <andre s-e-a-p.de> writes:
Hi,

following coding raises a compiler error with the beta of 2.067.
Is this error intended or not?
It is working if I change first line of main to: ulong bits;

enum Bits: ulong
{
	none = 0
}

bool hasBit(ref ulong rBits, ulong rBit)
{
	return cast(bool)(rBits & rBit);
}

void main()
{
	Bits bits;
	hasBit(bits, Bits.none);
}

function app.hasBit (ref ulong rBits, ulong rBit) is not callable 
using argument types (Bits, Bits)

Kind regards
André
Mar 10 2015
parent reply "Meta" <jared771 gmail.com> writes:
On Tuesday, 10 March 2015 at 07:04:48 UTC, Andre wrote:
 Hi,

 following coding raises a compiler error with the beta of 2.067.
 Is this error intended or not?
 It is working if I change first line of main to: ulong bits;

 enum Bits: ulong
 {
 	none = 0
 }

 bool hasBit(ref ulong rBits, ulong rBit)
 {
 	return cast(bool)(rBits & rBit);
 }

 void main()
 {
 	Bits bits;
 	hasBit(bits, Bits.none);
 }

 function app.hasBit (ref ulong rBits, ulong rBit) is not 
 callable using argument types (Bits, Bits)

 Kind regards
 André
It's because enums are not implicitly convertible to their base type. It was probably a compiler bug that it worked before. It's a regression however, so I'll file an issue in Bugzilla. In the meantime you can do: hasBit(cast(ulong)bits, Bits.none); Or just use a ulong as you mentioned.
Mar 10 2015
parent reply Jonathan M Davis via Digitalmars-d-learn writes:
On Tuesday, March 10, 2015 08:19:27 Meta via Digitalmars-d-learn wrote:
 On Tuesday, 10 March 2015 at 07:04:48 UTC, Andre wrote:
 Hi,

 following coding raises a compiler error with the beta of 2.067.
 Is this error intended or not?
 It is working if I change first line of main to: ulong bits;

 enum Bits: ulong
 {
     none = 0
 }

 bool hasBit(ref ulong rBits, ulong rBit)
 {
     return cast(bool)(rBits & rBit);
 }

 void main()
 {
     Bits bits;
     hasBit(bits, Bits.none);
 }

 function app.hasBit (ref ulong rBits, ulong rBit) is not
 callable using argument types (Bits, Bits)

 Kind regards
 Andr
It's because enums are not implicitly convertible to their base type. It was probably a compiler bug that it worked before. It's a regression however, so I'll file an issue in Bugzilla. In the meantime you can do: hasBit(cast(ulong)bits, Bits.none); Or just use a ulong as you mentioned.
enums _are_ implicitly convertible to their base type. e.g. this compiles just fine void main() { enum S : string { a = "hello", b = "world" } string s = S.a; } It's the base type that isn't implicitly convertible to the enum type. However, the code in question still shouldn't compile because while a Bits variable may be implicitly convertible to ulong, it _isn't_ a ulong, so passing it as a ref argument of type ulong isn't legal. Implicit conversions aren't used with ref. With ref, the type must match exactly. - Jonathan M Davis
Mar 10 2015
next sibling parent reply "Meta" <jared771 gmail.com> writes:
On Tuesday, 10 March 2015 at 08:37:46 UTC, Jonathan M Davis wrote:
 It's the base type that isn't implicitly convertible to the 
 enum type.
Err, yes. I had that the wrong way around. Anyway, I filed an issue. https://issues.dlang.org/show_bug.cgi?id=14269
Mar 10 2015
parent "Andre" <andre s-e-a-p.de> writes:
Thanks a lot!

Kind regards
André


On Tuesday, 10 March 2015 at 09:25:02 UTC, Meta wrote:
 On Tuesday, 10 March 2015 at 08:37:46 UTC, Jonathan M Davis 
 wrote:
 It's the base type that isn't implicitly convertible to the 
 enum type.
Err, yes. I had that the wrong way around. Anyway, I filed an issue. https://issues.dlang.org/show_bug.cgi?id=14269
Mar 10 2015
prev sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 03/10/2015 01:37 AM, Jonathan M Davis via Digitalmars-d-learn wrote:

 However, the code in question still shouldn't compile because while a 
Bits
 variable may be implicitly convertible to ulong, it _isn't_ a ulong,
In other words, the result of the implicit conversion is an rvalue, created on the spot, not the actual lvalue. References cannot be bound to rvalues. Ali
Mar 10 2015
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 03/10/2015 11:05 AM, Ali Çehreli wrote:

 In other words, the result of the implicit conversion is an rvalue
Steven Schveighoffer says there is no rvalue in this case; "an enum is a derivative": https://issues.dlang.org/show_bug.cgi?id=14269#c14 Ali
Mar 10 2015
parent Jonathan M Davis via Digitalmars-d-learn writes:
On Tuesday, March 10, 2015 13:26:00 Ali ehreli via Digitalmars-d-learn wrote:
 On 03/10/2015 11:05 AM, Ali ehreli wrote:

 In other words, the result of the implicit conversion is an rvalue
Steven Schveighoffer says there is no rvalue in this case; "an enum is a derivative": https://issues.dlang.org/show_bug.cgi?id=14269#c14
Implicit conversions result in rvalues, not lvalues. What's potentially different about enums is that underneath the hood, there's no difference between an enum and its base type - they're represented exactly the same in terms of bits; it's just the type system that treats them differently. So, the implicit conversion just changes how the type system treats it rather than the object's representation. So, it's possible to make it work so that a ref argument of the base type accepts a variable of the enum type, whereas that doesn't work with something like classes or even different integral types. An implicit conversion of an enum variable to its base type is one of the few cases where you even _could_ have an implicit conversion involving ref, but implicit conversions are supposed to result in rvalues as far as D's type system is concerned, so the fact that you could pass an enum value to a function taking its base type as a ref argument was definitely a bug. - Jonathan M Davis
Mar 11 2015