On Sunday, 8 April 2018 at 07:22:19 UTC, Patrick Schluter wrote:
You may find an in-depth discussion of the C++ case in
https://stackoverflow.com/questions/7499400/ternary-conditional-and-assignment-operator-precedence
My formulation was ambiguous, it is the same precedence as the
link says. The link also says that's it's right to left
evaluation. This means that for expression:
a ? b = c : d = e;
right to left evaluation will make the = e assignment higher
priority than the b = c assignment or the ternary even if they
have the same priority level.
To summarize: C++ works as expected and C prevents the assigment
because the conditional operator does not yield an l-value:
ccondo1.c
---
int main ()
{
int a, b;
1 ? a = 1 : b = 2;
return 0;
}
---
$ cc ccondo1.c
ccondo1.c: In function 'main':
ccondo1.c:4: error: lvalue required as left operand of assignment
Other languages:
----------------
- go: has no ternary conditional
- Java: Same as in C, example does not compile due to missing
l-value.
- JS: Like C++ (!).
https://www.ecma-international.org/ecma-262/6.0/#sec-conditional-operator
"The grammar for a ConditionalExpression in ECMAScript is
slightly different from that in C and Java, which each allow the
second subexpression to be an Expression but restrict the third
expression to be a ConditionalExpression. The motivation for this
difference in ECMAScript is to allow an assignment expression to
be governed by either arm of a conditional and to eliminate the
confusing and fairly useless case of a comma expression as the
centre expression."
