nonlvalue

A nonlvalue refers to an expression in programming languages, particularly those with lvalue and rvalue distinctions, that does not represent a modifiable memory location. In C++ and similar languages, an lvalue expression can appear on the left-hand side of an assignment operation, signifying that it refers to an object with a distinct identity and a memory address. Conversely, a nonlvalue, often called an rvalue, typically represents a temporary value or a value that cannot be directly modified.

Examples of nonlvalues include literal values, such as `5` or `"hello"`, and the results of most arithmetic operations, like `x + y`. These expressions produce a value but do not designate a specific, persistent storage location that can be reassigned. Function call results can also be nonlvalues if they return by value. The distinction is crucial for understanding memory management, object lifetimes, and optimization techniques like move semantics, which specifically leverage the temporary nature of nonlvalues. While some nonlvalues are inherently unmodifiable, the term primarily focuses on their inability to be assigned to.