[Issue 17141] CommonType!(dchar, char) returns uint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17141

Jack Stouffer  changed:

   What|Removed |Added

 Blocks||17358

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[Issue 17141] CommonType!(dchar, char) returns uint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17141

Jack Stouffer  changed:

   What|Removed |Added

   Severity|major   |critical

--- Comment #7 from Jack Stouffer  ---
Raising this to critical because this is actually a bug in DMD's type inference
and not a Phobos bug.

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[Issue 17141] CommonType!(dchar, char) returns uint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17141

--- Comment #5 from hst...@quickfur.ath.cx ---
Hmph.  Looks like the problem is that the very first thing typeMerge() does is
to do integer promotion on the incoming types. Thus, right from the start,
we've already lost the original character types. The only reason this hasn't
shown up earlier is because when the two types are equal, typeMerge() is not
called. So we're essentially only saved "by accident".

Oddly enough, there is an `if (op != TOKquestion || ...)`, which *seems* to
suggest that the intent of the code is *not* to do integer promotions if ?: is
involved. However, the second clause of the if condition, `t1b.ty != t2b.ty`,
appears to be always true, so the check for ?: would appear to be always
irrelevant.  It would seem that && was intended here rather than ||, but I've
to look more carefully to make sure this isn't going to cause massive code
breakage...

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[Issue 17141] CommonType!(dchar, char) returns uint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17141

--- Comment #4 from hst...@quickfur.ath.cx ---
Looks like this is implemented in the hairball function typeMerge() in
src/ddmd/dcast.d.  I'll try to trace through and see if I can find an obvious
problem, but I'm not sure if I'll be able to.

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[Issue 17141] CommonType!(dchar, char) returns uint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17141

hst...@quickfur.ath.cx changed:

   What|Removed |Added

  Component|phobos  |dmd

--

[Issue 17141] CommonType!(dchar, char) returns uint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17141

--- Comment #3 from hst...@quickfur.ath.cx ---
Unfortunately, it looks like CommonType is implemented using the ?: ternary
operator, meaning that it's the *compiler* that's producing these crazy
results.

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[Issue 17141] CommonType!(dchar, char) returns uint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17141

hst...@quickfur.ath.cx changed:

   What|Removed |Added

 CC||hst...@quickfur.ath.cx

--- Comment #2 from hst...@quickfur.ath.cx ---
It's not just CommonType!(dchar, char); it's a whole slew of cases that are
incorrectly handled:


void main() {
import std.range;

struct CharRange(C) {
C ch = 'a';
@property C front() { return ch; }
@property bool empty() { return ch == C.init; }
void popFront() { ch = C.init; }
}

CharRange!char charRange;
CharRange!wchar wcharRange;
CharRange!dchar dcharRange;

pragma(msg, "char + char: ", ElementType!(typeof(chain(charRange,
charRange;
pragma(msg, "char + wchar: ", ElementType!(typeof(chain(charRange,
wcharRange;
pragma(msg, "wchar + char: ", ElementType!(typeof(chain(wcharRange,
charRange;
pragma(msg, "char + dchar: ", ElementType!(typeof(chain(charRange,
dcharRange;
pragma(msg, "dchar + char: ", ElementType!(typeof(chain(dcharRange,
charRange;
pragma(msg, "wchar + wchar: ", ElementType!(typeof(chain(wcharRange,
wcharRange;
pragma(msg, "wchar + dchar: ", ElementType!(typeof(chain(wcharRange,
dcharRange;
pragma(msg, "dchar + wchar: ", ElementType!(typeof(chain(dcharRange,
wcharRange;
pragma(msg, "dchar + dchar: ", ElementType!(typeof(chain(dcharRange,
dcharRange;
}


Output:

char + char: char
char + wchar: int
wchar + char: int
char + dchar: uint
dchar + char: uint
wchar + wchar: wchar
wchar + dchar: uint
dchar + wchar: uint
dchar + dchar: dchar


Seems like the only time the correct common type is deduced, as far as
character types are concerned, is when both are types are the same. All the
other cases are worthy of a WAT?.

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[Issue 17141] CommonType!(dchar, char) returns uint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17141

Jack Stouffer  changed:

   What|Removed |Added

   Severity|normal  |major

--- Comment #1 from Jack Stouffer  ---
Raising the priority of this because chain is really gimped by this bug. Every
call to chain with character ranges requires an extra call to map to cast the
results for it to work correctly.

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