What Does "Name Collision" Mean?

Within the context of computers and computer programming, "name collision" is the technical term for an instance in which two items have the same name within some logical enclosure. A name collision can occur in many instances, such as with the names of files in a directory, or in a program in which local variables in a function have the same name as some global variables. Most of the time, a name collision must be resolved immediately in some way, whether automatically by an operating system or compiler or manually through user input and decisions. The concept of a namespace sometimes resolves collision issues by creating different logical regions in which items with similar names can co-exist without ambiguity. In certain programming instances, a name collision might not be immediately evident, occasionally leading to hard-to-find program errors that can result from the compiler making certain assumptions about the names of items used.

An example of how a name collision can occur involves two directories full of files. If each directory contains a file named "DATA", and the contents of one directory are copied into the other, then the computer's attempts to copy the file named DATA will find that a file with the same name already exists in the target directory. This creates a name collision. In this instance, the user usually will be prompted and allowed to choose from a list of resolutions, including renaming one of the files, not copying the file or overwriting one of the files.

One commonly used solution for a name collision is the implementation of namespaces. A namespace is simply a way to define an area under which object names are contained. In the above example, a directory technically is a namespace, meaning multiple files can all have the same name as long as they are each in different directories.

From a programming perspective, a name collision can occur in situations such as multiple inheritance, overlapping variable scopes, or even with imported libraries in some languages. In general, a compiler will notice a conflict and generate a warning or error, although this might not always be the case. Other than using namespaces, collisions in many programming languages can be avoided by using qualifiers. A qualifier usually is a prefix that can be placed in front of a variable or class name to distinguish it from another variable with the same name.