Type Safety - Relation To Other Forms of Safety

Relation To Other Forms of Safety

Type safety is ultimately aimed at excluding other problems, e.g.:-

  • Prevention of illegal operations. For example, we can identify an expression 3 / "Hello, World" as invalid, because the rules of arithmetic do not specify how to divide an integer by a string. As discussed below, strong typing offers more safety, but generally does not guarantee complete safety.
  • Memory safety
    • Wild pointers can arise when a pointer to one type object is treated as a pointer to another type. For instance, the size of an object depends on the type, so if a pointer is incremented under the wrong credentials, it will end up pointing at some random area of memory.
    • Buffer overflow - Out-of bound writes can corrupt the contents of objects already present on the heap. This can occur when a larger object of one type is crudely copied into smaller object of another type.
  • Logic errors originating in the semantics of different types. For instance, inches and millimeters may both be stored as integers, but should not be substituted for each other or added. A type system can enforce two different types of integer for them.

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