Unit (programming language Pascal)

A unit is a source code file that is compiled separately . Units have already been introduced in UCSD Pascal (see also Apple Pascal ). One unit consists of a public interface ( interface ) and a private implementation part ( implementation ). They are used to modularize software components and enable the reusability of program parts that are required in different programs.

In the public part, the interface of a unit, types (including classes , constants, variables and routines (functions and procedures)) can be declared. A unit can later be used as a library in other programs via a linker .

example

unit InetTools;  // Name der Unit


interface  
uses Classes, Windows;


function DownLoadInternetFile(const Source, Dest : String): Boolean;


implementation  // ab hier beginnt der ''private'' Teil


function DownLoadInternetFile(const Source, Dest : String): Boolean;
begin
   Result := URLDownloadToFile(nil, PChar(Source), PChar(Dest), 0 ,nil) = 0
end;


end.

The unit concept allows the compiler to create a dependency test in the background so that mutual dependencies can be recognized automatically and several units can be compiled at once. If z. For example, if the interface of unit A changes, the compiler has to compile all units that use this unit. If, on the other hand , changes have only taken place in the implementation , only unit A needs to be recompiled.

The foundation stone for the unit concept was laid by Modula-2 in 1982 with the compilation units .