In computer programming, name binding is the association of a data or code entity with an identifier. An identifier bound to an entity is said to reference that entity. A machine language has no built-in notion of identifiers, but name-entity binding as a service and notation for the programmer is implemented by higher-level programming languages. Binding is intimately connected with scoping, as scope determines which names bind to which entities â at which locations in the program code (lexically) and in which one of the possible execution paths (temporally).
Use of an identifier in a context that establishes a binding for is called a binding (or defining) occurrence. In all other occurrences (e.g., in expressions, assignments, and subprogram calls), an identifier stands for what it is bound to; such occurrences are called applied occurrences.
Rebinding should not be confused with mutation or assignment. Rebinding is a change to the referencing identifier. Assignment is a change to (the referenced) variable. Mutation is a change to an entity in memory, possibly referenced by a variable or bound to an identifier.
Consider the following Java code:
The identifier <code>list</code> is bound to a variable in the first line; in the second, a linked list of strings is assigned to the variable. The linked list referenced by the variable is then mutated, adding a string to the list. Next, the variable is assigned the constant <code>null</code>. In the last line, the identifier is rebound for the scope of the block. Operations within the block access a new variable and not the variable previously bound to <code>list</code>.