singleassignment

Single assignment is a programming concept where a variable is assigned a value only once. Once a variable has been assigned a value, it cannot be reassigned to a different value. This restriction applies at the language level, meaning the compiler or interpreter enforces it.

Languages that support single assignment, often referred to as "single-assignment languages" or "immutable variable languages," promote a functional programming style. In such languages, variables behave more like constants after their initial definition. If a new value is needed, a new variable must be declared.

The benefits of single assignment include increased predictability and easier reasoning about program state. Since a variable's value never changes, it simplifies debugging and can enable more aggressive compiler optimizations. This is because the compiler can be certain that the value of a variable will not be altered unexpectedly elsewhere in the program.

While many mainstream languages like Python, Java, and C++ do not strictly enforce single assignment for all variables, they do have constructs that mimic this behavior. For instance, the `final` keyword in Java or `const` in JavaScript and C++ allow for variables that are initialized once and then cannot be reassigned. Some functional programming languages, such as Haskell, inherently favor immutability and single assignment. Logic programming languages like Prolog also operate on a single assignment principle.