Essentials of Javascript - Cultural View

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C Variants
A GNU extension to C allows the second operand to be omitted, and the first operand is implicitly used as the
second as well:
a = x ? : y;
The expression is equivalent to
a = x ? x : y;
except that if x is an expression, it is evaluated only once. The difference is significant if evaluating the expression
has side effects.
C# (and Perl) provide similar functionality with their coalescing operator
a= x ?? y;
(Unlike the above usage of "x ?: y", ?? will only test if x is non-null, as opposed to non-false.)
C++
In C++ there are conditional assignment situations where use of the if-else statement is not possible, since this
language explicitly distinguishes between initialization and assignment. In such case it is always possible to use a
function call, but this can be cumbersome and inelegant. For example, if you want to pass conditionally different
values as an argument for a constructor of a field or a base class, it is not possible to use a plain if-else statement; in
this case we can use a conditional assignment expression, or a function call. Mind also that some types allow
initialization, but do not allow assignment, or even the assignment operator does totally different things than the
constructor. The latter is true for reference types, for example:
#include
#include
#include
using namespace std;
int main(int argc, char *argv[])
{
}
string name;
ofstream fout;
if (argc > 1 && argv[1])
{
}
name = argv[1];
fout.open(name.c_str(), ios::out | ios::app);
ostream &sout = name.empty() ? cout : fout;
In this case there's no possibility to replace the use of ?: operator with if-else statement. (Although we can replace the
use of ?: with a function call, inside of which can be an if-else statement.)