Wednesday, March 4, 2009

Type checking in programming languages

To discuss type checking in programming languages we have to define type checking. Simply,Type checking is how type errors are checked.

Type checking could happen at compile-time or at run-time. When type checking happens at the compile-time it is called Static Type Checking. When type checking happens at the run-time it is called Dynamic Type Checking.

Programming Languages differs in

  • when they check types.
  • Were it enforces types or not.

Based on these two factors, programming languages could be classified from the type checking perspective into the following classes:

Statically Typed Languages

In these languages, types are fixed at compile time. Most statically typed languages enforce this by requiring you to declare all variables with their data types before using them

C, Java, and C# are statically typed languages.

Dynamically Typed Languages

In these languages, types are discovered at execution time; the opposite of statically typed languages. These languages figure out what type a variable is when you first assign it a value.

VBScript and Python are dynamically typed languages.

Strongly Typed Languages

In these languages, types are always enforced. If you have an integer, you can’t treat it like a string without explicitly converting it.

Java and Python are strongly typed languages.

Weakly Typed Languages

In these languages, types may be ignored; the opposite of strongly typed languages. In VBScript, you can concatenate the string ‘12’ and the integer 3 to get the string ‘123’, then treat that as the integer 123, all without any explicit conversion.

VBScript is weakly typed language.

Programming languages could be classified based on many other factors and differences which we may discuss in further posts.

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