The Delphi Language, Part 1 - Delphi Language Types

(Page 4 of 10 )

One of the Delphi language's greatest features is that it's strongly typed, making it an excellent fit for the .NET platform. This means that actual variables passed to procedures and functions must be of the same type as the formal parameters identified in the procedure or function definition—very little is done for you in terms of implicit type conversion. Delphi's strongly-typed nature enables it to perform a sanity check of your code—to ensure that you aren't trying to put a square peg in a round hole. After all, the easiest bug fixes are the ones the compiler tells you to perform!

Objects, Objects Everywhere!

One of the most important notions regarding fundamental types in the .NET version of the Delphi compiler is that they are all value types capable of implicit conversion to classes. This conversation between value and object and back again is known as boxing and unboxing in .NET parlance. Integers, strings, floating points, and all of the rest are not implemented as primitive concepts in the compiler, as in Win32, but instead map to value types provided either by the .NET Framework or by Borland's RTL or VCL. Unlike Win32 Delphi, these value types can have their own procedures and functions in addition to those available in corresponding classes created by the implicit boxing and unboxing of these types. This allows for a kind of syntax that might be foreign for those coming from native compilers (although perhaps familiar for those experienced with languages such as Java or SmallTalk):

var
  S: string;
  I: Integer;
begin
  I := 42;
  S := I.ToString; // can call a method on an Integer!
end;

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Note - The string type is used heavily in development. This is not to say that other types are not, but there are some special considerations when using strings. Chapter 11 addresses strings specifically; therefore, you will not see detailed coverage of them here.

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A Comparison of Types

Delphi surfaces most of the primitive types available in the CLR. Table 5.5 compares and contrasts the base types of the Delphi language with those of C# and the CLR. This table also indicates whether each type is compliant with the CLS.

Table 5.5 A Delphi-to-C#-to-CLR Type Comparison

Variable range	Delphi	C#	CLR	CLS Compliant?
8-bit signed integer	ShortInt	sbyte	System.SByte	No
8-bit unsigned integer	Byte	byte	System.Byte	Yes
16-bit signed integer	SmallInt	short	System.Int16	Yes
16-bit unsigned integer	Word	ushort	System.UInt16	No
32-bit signed integer	Integer	int	System.Int32	Yes
32-bit unsigned integer	Cardinal	uint	System.UInt32	No
64-bit signed integer	Int64	long	System.Int64	Yes
64-bit unsigned integer	UInt64	ulong	System.UInt64	No
single precision float	Single	float	System.Single	Yes
double precision float	Double	double	System.Double	Yes
fixed-point decimal	None	decimal	System.Decimal	Yes
Delphi fixed-point decimal	Currency	None	None	No
date/time	TDateTime*	None	System.DateTime	Yes
variant	Variant, OleVariant	None	None	No
1-byte character	AnsiChar	None	None	No
2-byte character	Char, WideChar	char	System.Char	Yes
Fixed-length byte string	ShortString	None	None	No
Dynamic 1-byte string	AnsiString	None	None	No
Dynamic 2-byte string	string, WideString	string	System.String	Yes
Boolean	Boolean	bool	System.Boolean	None

*TDateTime is a record that wraps a System.DateTime with methods and operator overloads that makes it behave very much like System.DateTime , but with additional behavior to be compatible with Win32 Delphi's TDateTime type. 

Characters

Delphi provides three character types:

• WideChar—This CLS-compatible character is two bytes in size and represents a Unicode character.

• Char—This is an alias for WideChar. In Win32 versions of Delphi, Char was an AnsiChar.

• AnsiChar—An old school one-byte ANSI character.

Never assume the size of a Char (or any other type, for that matter), in your code. Instead, you should use the SizeOf() function where appropriate.

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Note - The SizeOf() standard procedure returns the size, in bytes, of a type or variable.

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This chapter is from Delphi for .NET Developer's Guide, by Xavier Pacheco (Sams, 2004, ISBN: 0-672-32443-1). Check it out at your favorite bookstore today. Buy this book now.

Next: Variant Types >>
 

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