#typesystem

In Program Languages the "type system" is a rules set that provides the ability to determine a type for commands, expressions and other languages constructs. There are many types of languages and everyone could have a different type system but we can summarize them into 2 families:

- Statically Typed: when all types can be defined at compile-time (analyzing the source code) - Dinamically Typed: in the other cases, when the type can't be determined only analyzing the source but it depends on execution state

Example: PHP code

$a = 100; // This instruction defines an integer variable

Afterwards we could re-define the $a variable as array

$a[1] = 100; // The variable must be an array

The latter instruction will run successfully only if $a is an array, for executing this code the PHP engine must do a dynamic type checking. In fact PHP has a dynamic type system that provides a great flexibility to the language however it forces the engine to make continous checking. The statically typed languages are obviously much more efficient than the dynamic ones (all types are binded at compile time and they don't need to redo the checking at runtime), however dynamic typed languages can rely on the flexibility from the dynamic world.

This post are only showing the basics of the type system and is intended to whet the curiosity on the deeper world inside programming stuff.