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5-30

Delphi Language Guide

Procedural types

Procedural types allow you to treat procedures and functions as values that can be

assigned to variables or passed to other procedures and functions. For example,

suppose you define a function called Calc that takes two integer parameters and

returns an integer:

function Calc(X,Y: Integer): Integer;

You can assign the Calc function to the variable F:

var F: function(X,Y: Integer): Integer;

F := Calc;

If you take any procedure or function heading and remove the identifier after the

word procedure or function, what’s left is the name of a procedural type. You can

use such type names directly in variable declarations (as in the previous example) or

to declare new types:

type

TIntegerFunction = function: Integer;

TProcedure = procedure;

TStrProc = procedure(const S: string);

TMathFunc = function(X: Double): Double;

var

F: TIntegerFunction; { F is a parameterless function that returns an integer }

Proc: TProcedure; { Proc is a parameterless procedure }

SP: TStrProc; { SP is a procedure that takes a string parameter }

M: TMathFunc; { M is a function that takes a Double (real) parameter

and returns a Double }

procedure FuncProc(P: TIntegerFunction); { FuncProc is a procedure whose only parameter

is a parameterless integer-valued function }

PShortString ShortString. Useful when porting legacy code that uses the old PString

type.

PTextBuf TTextBuf (declared in SysUtils). TTextBuf is the internal buffer type in a

TTextRec file record.)

PVarRec TVarRec (declared in System)

PVariant Variant

PWideString WideString

PWordArray TWordArray (declared in SysUtils). Used to typecast dynamically

allocated memory for arrays of 2-byte values.

Table 5.6 Selected pointer types declared in System and SysUtils (continued)

Pointer type Points to variables of type