digitalmars.D.bugs - [Issue 8143] New: Safe std.conv.to enum conversion
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http://d.puremagic.com/issues/show_bug.cgi?id=8143
Summary: Safe std.conv.to enum conversion
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: Phobos
AssignedTo: nobody puremagic.com
ReportedBy: bearophile_hugs eml.cc
import std.conv: to;
enum Foo : int { A = 10, B = 20 }
void main() {
int x = 10;
Foo f1 = to!Foo(x);
assert(f1 == Foo.A);
x = 5;
Foo f2 = to!Foo(x); // needs to throw an exception
}
DMD 2.060alpha gives:
...\dmd2\src\phobos\std\conv.d(267): Error: template std.conv.toImpl does not
match any function template declaration
...\dmd2\src\phobos\std\conv.d(298): Error: template std.conv.toImpl cannot
deduce template function from argument types !(Foo)(int)
...\dmd2\src\phobos\std\conv.d(267): Error: template instance toImpl!(Foo)
errors instantiating template
temp.d(5): Error: template instance std.conv.to!(Foo).to!(int) error
instantiating
This is handy to *safely* convert run-time values to enum items. Using a
cast(Foo) is useful in other cases, because cast(Foo) doesn't raise a run-time
exceptions. The same difference is visible in this program:
import std.conv: to;
void main() {
int x = -10;
uint y1 = cast(uint)x; // no errors here
uint y2 = to!uint(x); // throws std.conv.ConvOverflowException
}
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May 24 2012
d-bugmail puremagic.com
http://d.puremagic.com/issues/show_bug.cgi?id=8143
Andrej Mitrovic <andrej.mitrovich gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |andrej.mitrovich gmail.com
16:44:27 PDT ---
One problem with this is:
enum EF : float { C = 4.9 }
float f = 4.9;
EF en2 = to!EF(f);
This will fail internally if conv.to compares members via "==", because of
floating point comparison semantics.
So the question is, is this going to be a problem? If yes, should we use
approxEqual for floating point comparisons? Or maybe we should simply ban using
std.conv on enums that have a floating point base type?
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Oct 23 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143This will fail internally if conv.to compares members via "==", because of floating point comparison semantics. So the question is, is this going to be a problem? If yes, should we use approxEqual for floating point comparisons?By far the main purpose of enums is with integral values (ints, uint, chars, etc), to be used to enumerate something or as bitfields. Using float/double/real enums is supported in D, but it's not common. Using approxEqual is suboptimal, using std.math.feqrel is better. but all approximate floating point comparisons have their quirks and limits. Backing-in one solution is not a good idea.Or maybe we should simply ban using std.conv on enums that have a floating point base type?What about user-defined floating point types, or a double wrapped in a struct with an alias this? I think refusing conv on built-in floating point types is an acceptable solution to avoid most troubles. Other cases like wrapped doubles are left at the care of the programmer. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 23 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143
monarchdodra gmail.com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |monarchdodra gmail.com
This will fail internally if conv.to compares members via "==", because of
floating point comparison semantics.
So the question is, is this going to be a problem? If yes, should we use
approxEqual for floating point comparisons?
By far the main purpose of enums is with integral values (ints, uint, chars,
etc), to be used to enumerate something or as bitfields. Using
float/double/real enums is supported in D, but it's not common.
Using approxEqual is suboptimal, using std.math.feqrel is better. but all
approximate floating point comparisons have their quirks and limits. Backing-in
one solution is not a good idea.
Or maybe we should simply ban using
std.conv on enums that have a floating point base type?
What about user-defined floating point types, or a double wrapped in a struct
with an alias this?
I think refusing conv on built-in floating point types is an acceptable
solution to avoid most troubles. Other cases like wrapped doubles are left at
the care of the programmer.
I'd say there is nothing wrong with using floats as enums. It's rare because
it's new (C++ only supported integral up to now). In C++, I've seen integral
based enums used to index arrays which contained the actual payload (floats,
strigns, others). Now we don't have to do this anymore.
The *real* issue (IMO) is only when converting *back* from float to enum, which
(IMO again), is plain too dangerous to realisticly assume we can support.
I'd rather have float-to-enum always fail, personally.
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Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143
08:02:31 PDT ---
Or alternatively require an additional alias parameter for the comparison
function in case of floats?
E.g.
enum EF : float { C = 4.9 }
float f = 4.9;
static bool compFunc(float lhs, float rhs) { ... }
EF en2 = to!(EF, compFunc)(f);
Since conv.to will already do the work necessary to 1) find the matching
member, 2) ensure there's only 1 matching member, I think customization like
this might be friendlier than just rejecting conversion.
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Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143
Andrej Mitrovic <andrej.mitrovich gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|nobody puremagic.com |andrej.mitrovich gmail.com
10:13:51 PDT ---
Ok here's a first implementation, let me know if it can be improved before a
pull request is made (the docs will be improved too):
External: http://dpaste.dzfl.pl/ee99ce99
And copied here:
import std.traits;
import std.conv : ConvException, assertThrown;
import std.string;
import std.math;
import std.stdio;
/**
Convert a value that is implicitly convertible to the enum base type
into an Enum value.
If the value does not match any enum member values, or
if it matches more than one member value throw a ConvException.
*/
T toImpl(T, S)(S value)
if (is(T == enum) && is(S : OriginalType!T) &&
!isFloatingPoint!(OriginalType!T))
{
T result;
size_t matches;
foreach (Member; EnumMembers!T)
{
if (Member == value)
{
result = Member;
if (++matches > 1)
throw new ConvException(format("Value (%s) matches more than
one member value of enum '%s'", value, fullyQualifiedName!T));
}
}
if (!matches)
throw new ConvException(format("Value (%s) does not match any member
value of enum '%s'", value, fullyQualifiedName!T));
return result;
}
/**
Ditto:
Specialization for Enums that have a floating point base type.
equal must be a function which takes the enum base type as
its first parameter, the type of value as its second parameter,
and return true if the two compare equal.
*/
T toImpl(T, alias equal, S)(S value)
if (is(T == enum) && is(S : OriginalType!T) &&
isFloatingPoint!(OriginalType!T))
{
T result;
size_t matches;
foreach (Member; EnumMembers!T)
{
if (equal(Member, value))
{
result = Member;
if (++matches > 1)
throw new ConvException(format("Value (%s) matches more than
one member value of enum '%s'", value, fullyQualifiedName!T));
}
}
if (!matches)
throw new ConvException(format("Value (%s) does not match any member
value of enum '%s'", value, fullyQualifiedName!T));
return result;
}
alias toImpl to;
void test()
{
enum En : int { A = 10, B = 20, C = 30, D = 20 }
En en1 = to!En(10);
assert(en1 == En.A);
assertThrown!ConvException(to!En(5));
// matches more than one
assertThrown!ConvException(to!En(20));
static bool equal(float a, float b) { return feqrel(a, b) >= 24; }
enum EF : float { C = 4.9 }
float f = 4.9;
EF enf = to!(EF, equal)(f);
enum EF2 : float { A = 4.9, B = 1.0, C = 4.9 }
float f2 = 4.9;
// matches more than one
assertThrown!ConvException(to!(EF2, equal)(f2));
}
void main()
{
test();
}
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Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143
bearophile_hugs eml.cc changed:
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|andrej.mitrovich gmail.com |nobody puremagic.com
I think customization like
this might be friendlier than just rejecting conversion.
It also makes the implementation and usage a bit more complex. Ask to other
people (like Andrei) to see what they think. (Here my preference goes to a
simple solution).
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Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143Ok here's a first implementation, let me know if it can be improved before a pull request is made (the docs will be improved too):One more test case: En[][] m1 = to!(En[][])([[10, 30], [30, 10]]); Have you compiled your code with "-property -w"? I am seeing some errors: ...\dmd2\src\phobos\std\traits.d(221): Error: not a property test ...\dmd2\src\phobos\std\traits.d(225): Error: not a property test ...\dmd2\src\phobos\std\traits.d(229): Error: not a property test ...\dmd2\src\phobos\std\traits.d(234): Error: not a property test ...\dmd2\src\phobos\std\traits.d(231): Error: template instance std.traits.fullyQualifiedName!(test) error instantiating test.d(27): instantiated from here: fullyQualifiedName!(En) test.d(76): instantiated from here: toImpl!(En,int) test.d(27): Error: template instance std.traits.fullyQualifiedName!(En) error instantiating test.d(76): instantiated from here: toImpl!(En,int) test.d(26): Error: constructor std.conv.ConvException.this (string s, string fn = __FILE__, uint ln = cast(uint)__LINE__) is not callable using argument types (_error_) test.d(26): Error: constructor std.conv.ConvException.this (string s, string fn = __FILE__, uint ln = cast(uint)__LINE__) is not callable using argument types (_error_) test.d(26): Error: constructor std.conv.ConvException.this (string s, string fn = __FILE__, uint ln = cast(uint)__LINE__) is not callable using argument types (_error_) test.d(26): Error: constructor std.conv.ConvException.this (string s, string fn = __FILE__, uint ln = cast(uint)__LINE__) is not callable using argument types (_error_) test.d(32): Error: constructor std.conv.ConvException.this (string s, string fn = __FILE__, uint ln = cast(uint)__LINE__) is not callable using argument types (_error_) test.d(76): Error: template instance test.toImpl!(En,int) error instantiating -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143 10:28:51 PDT ---It's only complex for the case of floating point conversion. We could by default set the alias to be a safe floating-point comparison function by default so the user doesn't have to pass one if he doesn't want to. There are other to!() implementations that take special arguments, e.g. in radix conversions an extra argument is passed. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------I think customization like this might be friendlier than just rejecting conversion.It also makes the implementation and usage a bit more complex. Ask to other people (like Andrei) to see what they think. (Here my preference goes to a simple solution).
Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143 10:31:14 PDT ---One more test case: En[][] m1 = to!(En[][])([[10, 30], [30, 10]]);Ah, haven't thought about arrays. Will fix..Have you compiled your code with "-property -w"? I am seeing some errors:Those seem to be Phobos errors, unrelated to my code. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143 One more test case: enum En[][] m1 = to!(En[][])([[10, 30], [30, 10]]); -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143 10:58:10 PDT --- http://dpaste.dzfl.pl/f4e35e84 More tests welcome! -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143http://dpaste.dzfl.pl/f4e35e84Please attach this in Bugzilla :-)More tests welcome!Is this supported? enum En[][] m1 = to!(En[][])([[10, 30], [30, 10]]); -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143 17:32:54 PDT --- Created an attachment (id=1153) dIs this supported? enum En[][] m1 = to!(En[][])([[10, 30], [30, 10]]);Yes. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143Then I suggest to add it to your tests, because it's not present. Your tests contain code like: En[][] m1 = to!(En[][])([[10, 30], [30, 10]]); -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------Is this supported? enum En[][] m1 = to!(En[][])([[10, 30], [30, 10]]);Yes.
Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143
Andrej Mitrovic <andrej.mitrovich gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
is obsolete| |
17:56:41 PDT ---
Created an attachment (id=1154)
code
Is this supported?
enum En[][] m1 = to!(En[][])([[10, 30], [30, 10]]);
Yes.
Then I suggest to add it to your tests, because it's not present.
Your tests contain code like:
En[][] m1 = to!(En[][])([[10, 30], [30, 10]]);
Ah it took me a while to realize you were looking for CTFE ability.
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http://d.puremagic.com/issues/show_bug.cgi?id=8143Ah it took me a while to realize you were looking for CTFE ability.Sorry for not being more clear. Another significant test case, this is useful in many simulations and games, to write safe tables and start conditions: enum Code : char { A='A', B='B', C='C' } void test() { ... const code = to!(Code[][])(["ABCCBA", "BBAA"]); with (Code) assert(code == [[A, B, C, C, B, A], [B, B, A, A]]); } The main problem with this is that you receive conversion errors only at run-time, and in D the problem with array compile-time constants is that the compiler re-creates them every time where you use them. So they are not so useful. ------------------ Unfortunately this is not yet allowed because to!() is not pure: immutable code = to!(Code[][])(["ABCCBA", "BBAA"]); -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143
Andrej Mitrovic <andrej.mitrovich gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
is obsolete| |
18:49:26 PDT ---
Created an attachment (id=1155)
new
Without purity it works ok though.
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Oct 24 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143 10:05:39 PDT ---Created an attachment (id=1155) [details] new Without purity it works ok though.Not much (any) response in D NG. I could try and make a pull and see what folks have to say. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 25 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143Not much (any) response in D NG. I could try and make a pull and see what folks have to say.OK. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 25 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143
16:40:22 PDT ---
Another significant test case, this is useful in many simulations and games, to
write safe tables and start conditions:
enum Code : char { A='A', B='B', C='C' }
void test()
{
...
const code = to!(Code[][])(["ABCCBA", "BBAA"]);
with (Code)
assert(code == [[A, B, C, C, B, A], [B, B, A, A]]);
}
I won't be able to do this, the problem is there is already a toImpl overload
which takes a string and turns it into an enum. It has different semantics, it
searches for matching member names rather than member values.
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Oct 26 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143I won't be able to do this, the problem is there is already a toImpl overload which takes a string and turns it into an enum. It has different semantics, it searches for matching member names rather than member values.I see. See also Issue 5515 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 27 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8143
Andrej Mitrovic <andrej.mitrovich gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |pull
AssignedTo|nobody puremagic.com |andrej.mitrovich gmail.com
16:50:10 PST ---
https://github.com/D-Programming-Language/phobos/pull/1085
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Jan 21 2013
http://d.puremagic.com/issues/show_bug.cgi?id=8143 Commits pushed to master at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/72a09960890aedda14173304263c21ff3671262b Fixes Issue 8143 - Safe std.conv.to enum conversion https://github.com/D-Programming-Language/phobos/commit/f110604b593799f74af4cdedd6bd61c8275926e3 Fix Issue 8143 - Safe std.conv.to enum conversion -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 10 2013
http://d.puremagic.com/issues/show_bug.cgi?id=8143
Andrej Mitrovic <andrej.mitrovich gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
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http://d.puremagic.com/issues/show_bug.cgi?id=8143 Commit pushed to staging at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/e22fef3c36362aebd2c2fd60e344c32ec06dd0b3 Fixes Issue 8143 - Safe std.conv.to enum conversion -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 13 2013
http://d.puremagic.com/issues/show_bug.cgi?id=8143 15:05:24 PST --- *** Issue 5515 has been marked as a duplicate of this issue. *** -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 17 2013