zerovalue

Zero value is a term used in mathematics and computer science to describe the additive identity and, in programming, the default value a variable of a given type holds when it is declared without an explicit initial value. In mathematics, the zero element satisfies a + 0 = a for every element a in a structure such as a group or ring. In programming, the zero value provides a well-defined starting point for variables and helps prevent undefined behavior, though it is not the same as a null or missing value.

In many languages, each type has a specified zero value. Common examples include 0 for numeric types, false for booleans, and the empty string "" for text. For reference types such as pointers, interfaces, maps, slices, channels, and functions, the zero value is often nil (or an equivalent null-like value). For composite types, such as arrays and structs, the zero value is obtained by taking the zero value of each element or field.

Go language design highlights the concept of zero value explicitly. In Go, variables declared without an explicit initial value are assigned the zero value of their type: numbers become 0, booleans false, strings the empty string, and reference-like types such as pointers, slices, maps, interfaces, channels, and functions become nil. Other languages may use a similar defaulting mechanism or require explicit initialization, with varying semantics for what constitutes an absence of value.

Zero value is distinct from notions such as null, undefined, or optional values. It is a concrete value intrinsic to the type, used to ensure predictable behavior during variable initialization and operations. See also additive identity, default value, and nil.