The C compiler checks the types of the arguments passed to a function when it is called against the types of the parameters declared in the function's definition. If the instructions inside the function are written with the assumption of receiving an integer value, but the calling code passed a floating-point value, then the wrong result will be computed by the invoked function. The invoked function's code accesses the values and makes use of them. During execution, the values are placed into temporary storage, then execution jumps to the code of the invoked function. The code of an invoking function states the name of the invoked, along with the names of variables that hold values to pass to it. The interface of a function states the name of the function and a list of parameters that are passed to the function's code. One function is invoked by another function. The portions of a C program are the function definitions. 9 Compatibility: equivalence and subtypingĪn example of a simple type system is that of the C language.6 Explicit or implicit declaration and inference.3.4 Static and dynamic type checking in practice.3.3 Combining static and dynamic type checking.3.2 Dynamic type checking and runtime type information.Type systems are often specified as part of programming languages and built into interpreters and compilers, although the type system of a language can be extended by optional tools that perform added checks using the language's original type syntax and grammar. The given type system in question determines what constitutes a type error, but in general, the aim is to prevent operations expecting a certain kind of value from being used with values for which that operation does not make sense (validity errors).
Type systems have other purposes as well, such as expressing business rules, enabling certain compiler optimizations, allowing for multiple dispatch, providing a form of documentation, etc.Ī type system associates a type with each computed value and, by examining the flow of these values, attempts to ensure or prove that no type errors can occur. This checking can happen statically (at compile time), dynamically (at run time), or as a combination of both. The main purpose of a type system is to reduce possibilities for bugs in computer programs by defining interfaces between different parts of a computer program, and then checking that the parts have been connected in a consistent way. "string", "array of float", "function returning boolean"). These types formalize and enforce the otherwise implicit categories the programmer uses for algebraic data types, data structures, or other components (e.g. In programming languages, a type system is a logical system comprising a set of rules that assigns a property called a type to the various constructs of a computer program, such as variables, expressions, functions or modules.
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