Re: dmd-2.067.0-b1
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Re: dmd-2.067.0-b1
On Friday, 13 February 2015 at 09:38:04 UTC, Dennis Ritchie wrote:
This is a bug?
import std.stdio;
void main() {
int a = 0;
writeln( (a 10) ? a = 1 : a = 2 );// prints 2
writeln( (a 10) ? a = 1 : (a = 2) ); // prints 1
}
Even C++ output:
1
1
Maybe a similar issue as this:
http://forum.dlang.org/thread/wlpmjgbkdzcyuuyaf...@forum.dlang.org
Re: dmd-2.067.0-b1
On Friday, 13 February 2015 at 13:25:55 UTC, Steven Schveighoffer
wrote:
On 2/13/15 7:38 AM, tcak wrote:
On Friday, 13 February 2015 at 09:38:04 UTC, Dennis Ritchie
wrote:
This is a bug?
import std.stdio;
void main() {
int a = 0;
writeln( (a 10) ? a = 1 : a = 2 );// prints 2
writeln( (a 10) ? a = 1 : (a = 2) ); // prints 1
}
Even C++ output:
1
1
About 2 years ago, I had a problem with similar structure.
My guess is that the first one is accepted as this.
((a 10) ? a = 1 : a) = ( 2 )
Thereby it gives this result. Vague definitions are always
error prone.
Yes, the operator precedence (curiously not defined in the
spec) is here:
http://wiki.dlang.org/Operator_precedence
Conditional operator is above assignment operators.
C++ operator precedence is here:
http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B#Operator_precedence
Note they are the same, but I think C++ ?: = operator in this
case does not result in lvalue. So it must be that the = cannot
bind to the result of the operator, therefore it binds to the
a. Interesting...
-Steve
Thanks.
Re: dmd-2.067.0-b1
On Friday, 13 February 2015 at 13:25:55 UTC, Steven Schveighoffer wrote: Yes, the operator precedence (curiously not defined in the spec) is here: http://wiki.dlang.org/Operator_precedence Conditional operator is above assignment operators. It's specified through the grammar [1]: AssignExpression: ConditionalExpression ConditionalExpression = AssignExpression [...] ConditionalExpression: OrOrExpression OrOrExpression ? Expression : ConditionalExpression The third operand of ConditionalExpression cannot be an AssignExpression without parentheses. So `foo ? bar : baz = qux` can only be interpreted as `(foo ? bar : baz) = qux`. [1] http://dlang.org/expression.html
Re: dmd-2.067.0-b1
On 2/13/15 7:38 AM, tcak wrote:
On Friday, 13 February 2015 at 09:38:04 UTC, Dennis Ritchie wrote:
This is a bug?
import std.stdio;
void main() {
int a = 0;
writeln( (a 10) ? a = 1 : a = 2 );// prints 2
writeln( (a 10) ? a = 1 : (a = 2) ); // prints 1
}
Even C++ output:
1
1
About 2 years ago, I had a problem with similar structure.
My guess is that the first one is accepted as this.
((a 10) ? a = 1 : a) = ( 2 )
Thereby it gives this result. Vague definitions are always error prone.
Yes, the operator precedence (curiously not defined in the spec) is here:
http://wiki.dlang.org/Operator_precedence
Conditional operator is above assignment operators.
C++ operator precedence is here:
http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B#Operator_precedence
Note they are the same, but I think C++ ?: = operator in this case does
not result in lvalue. So it must be that the = cannot bind to the result
of the operator, therefore it binds to the a. Interesting...
-Steve
Re: dmd-2.067.0-b1
On 2/13/15 9:01 AM, anonymous wrote: On Friday, 13 February 2015 at 13:25:55 UTC, Steven Schveighoffer wrote: Yes, the operator precedence (curiously not defined in the spec) is here: http://wiki.dlang.org/Operator_precedence Conditional operator is above assignment operators. It's specified through the grammar [1]: AssignExpression: ConditionalExpression ConditionalExpression = AssignExpression [...] ConditionalExpression: OrOrExpression OrOrExpression ? Expression : ConditionalExpression The third operand of ConditionalExpression cannot be an AssignExpression without parentheses. So `foo ? bar : baz = qux` can only be interpreted as `(foo ? bar : baz) = qux`. [1] http://dlang.org/expression.html Right, but C++ seems to treat it differently, but has the same order of precedence. It seems that C++ can do lvalues as a result of assignment, but for some reason it doesn't do the same as D. Indeed, if you do: (a 10) ? 5 : a = 1; In D, this results in an error, in C++, this just results in the rvalue 5. OK, so I just looked for more information, and found that in some references, the ?: is given the same precedence as the assignment operator (and ordered right to left), which would explain the behavior. So likely the wikipedia reference is just wrong. e.g.: http://en.cppreference.com/w/cpp/language/operator_precedence Walter (or other language gurus), any reason that D does it this way? The C++ way seems more natural to me. -Steve
Re: dmd-2.067.0-b1
On Friday, 13 February 2015 at 09:38:04 UTC, Dennis Ritchie wrote:
This is a bug?
import std.stdio;
void main() {
int a = 0;
writeln( (a 10) ? a = 1 : a = 2 );// prints 2
writeln( (a 10) ? a = 1 : (a = 2) ); // prints 1
}
Even C++ output:
1
1
About 2 years ago, I had a problem with similar structure.
My guess is that the first one is accepted as this.
((a 10) ? a = 1 : a) = ( 2 )
Thereby it gives this result. Vague definitions are always error
prone.
