Is the Ternary Operator's Result an Lvalue or an Rvalue?

Ternary Conditional Operator and Its Result Lvalue or Rvalue

The ternary/conditional operator ('?:') provides a shorthand syntax for selecting one of two expressions based on a condition. Understanding the result type of this operator is crucial for various programming tasks.

Conditional Expression as Lvalue

The conditional operator returns an lvalue when the second and third operands are lvalues of the same type. This is observed when both operands (x and y) in the following code are integers:

int x = 1;
int y = 2;
(x > y ? x : y) = 100; // Assignment is allowed since the result is an lvalue

In this case, the conditional expression (x > y ? x : y) is an lvalue, which enables the subsequent assignment to 100.

Conditional Expression as Rvalue

However, when the second and third operands have different types, the conditional expression becomes an rvalue. This is evident in the following code:

int x = 1;
long y = 2;
(x > y ? x : y) = 100; // Error: Assignment is not allowed for rvalues

Due to implicit conversion of x to long to match the type of y, the conditional expression becomes an rvalue. Since rvalues are not modifiable, the assignment operation fails.

Determining the Result Type

The type and value category of a conditional expression are determined at compile time. It conforms to the following rules:

• If both operands are lvalues of the same type, the result is an lvalue of that type.
• If both operands are rvalues, the result is a prvalue (a type-erased rvalue).
• If one operand is an lvalue and the other is an rvalue, the result is an rvalue.

Understanding these rules ensures effective use of the ternary/conditional operator.

The above is the detailed content of Is the Ternary Operator's Result an Lvalue or an Rvalue?. For more information, please follow other related articles on the PHP Chinese website!