Exception safety

Exception safety guarantees, originally formalized by David Abrahams, are a set of contractual guidelines that class library implementers and clients can use when reasoning about exception handling safety in any programming language that uses exceptions, particularly C++.

There are several levels of exception safety (in decreasing order of safety):

Usually, at least basic exception safety is required to write robust code in such languages. Higher levels of safety can sometimes be difficult to achieve, and might incur an overhead due to extra copying. A key mechanism for exception safety is a finally clause, or similar exception handling syntax, which ensure that certain code is always run when a block is exited, including by exceptions. Several languages have constructs that simplify this, notably using the dispose pattern, named as using, with, or try-with-resources.

Consider a smart vector type, such as C++'s std::vector or Java's ArrayList. When an item x is added to a vector v, the vector must actually add x to the internal list of objects and update a count field that says how many objects are in v. It may also need to allocate new memory if the existing capacity isn't sufficient.

Exception safety alternatives:

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