digitalmars.D.learn - dmd-2.067.0-b1
- Dennis Ritchie (10/10) Feb 13 2015 This is a bug?
- tcak (6/16) Feb 13 2015 About 2 years ago, I had a problem with similar structure.
- Steven Schveighoffer (10/30) Feb 13 2015 Yes, the operator precedence (curiously not defined in the spec) is here...
- anonymous (17/21) Feb 13 2015 It's specified through the grammar [1]:
- Steven Schveighoffer (15/36) Feb 13 2015 Right, but C++ seems to treat it differently, but has the same order of
- Dennis Ritchie (3/41) Feb 13 2015 Thanks.
- Gary Willoughby (3/13) Feb 13 2015 Maybe a similar issue as this:
- RuZzz (2/2) Feb 14 2015 It is your profile?
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
Feb 13 2015
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.
Feb 13 2015
On 2/13/15 7:38 AM, tcak wrote:On Friday, 13 February 2015 at 09:38:04 UTC, Dennis Ritchie 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. 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... -SteveThis 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 1About 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.
Feb 13 2015
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
Feb 13 2015
Steven Schveighoffer <schveiguy yahoo.com> On 2/13/15 9:01 AM, anonymous wrote:On Friday, 13 February 2015 at 13:25:55 UTC, Steven Schveighoffer wrote: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. -SteveYes, 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
Feb 13 2015
On Friday, 13 February 2015 at 13:25:55 UTC, Steven Schveighoffer wrote:On 2/13/15 7:38 AM, tcak wrote:Thanks.On Friday, 13 February 2015 at 09:38:04 UTC, Dennis Ritchie 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. 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... -SteveThis 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 1About 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.
Feb 13 2015
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/wlpmjgbkdzcyuuyafzwk forum.dlang.org
Feb 13 2015
It is your profile? http://www.cyberforum.ru/members/491746.html
Feb 14 2015