[2. Basics of Delphi grammar] 1 Identifiers and reserved words

1. Identifiers and reserved words

stay Object Pascal in , Symbols consist of one or more characters , Is the most basic language element .

1.1 identifier

The identifier is ObjectPascal Variables in language 、 Constant 、 type 、 The process 、 function 、 Method 、 Name of unit, etc .

• Standard Identifier

  The standard identifier is ObjectPascal Language is pre assigned to standard functions 、 Standard process 、 Standard type 、 Standard constant 、 Identifiers used in standard documents .

  • Standard constant Such as ：False、True、Maxint etc.

  • Standard type Such as ：Boolean、Char、Real etc.

  • Standard functions Such as ：Sin、Cos、Abs、Arctan etc.

  • Standard process Such as ：Dispose、Get、New、Pack、Put etc.

  • Standard document Such as ：Input、Output etc.

• Custom identifier

  Custom identifiers are based on the needs of program design , Self defined constants 、 Variable 、 type 、 function 、 Name of process, etc . stay Object Pascal Rules for defining identifiers in ：

  1. Identifiers are case insensitive 
  2. Identifiers can only start with letters or underscores 
  3. Identifier can be any length , But only before 255 Characters are valid 
  4. No space is allowed between identifiers 
  5. Not allowed Object Pascal Reserved word as identifier 

• Qualified identifier

  stay Object Pascal Multiple units can be referenced in , And the global variables in each unit 、 function 、 Process, etc. may have the same name , therefore , When referenced in the program, you need to use qualified identifiers to distinguish . Such as ：

  Var
  Y: real;
  Y := System.cos(pi);

  In code System Is the qualified identifier , limit cos The identifier is System The identifier declared in the unit .

1.2 Reserved words

Reserved words are specified by the system , Words with special meanings and uses , It cannot be redefined in programming .Object Pascal It defines 65 A reserved word ：

Reserved words
and	array	as	asm	begin	case
class	Const	constructor	destructor	dispinterface	div
do	downto	else	end	except	exports
file	finalization	finally	for	function	goto
if	implementation	in	inherite	initialization	inline
is	interface	label	library	mod	Nil
not	object	of	or	out	packed
procedure	program	property	raise	record	repeat
resourcestring	set	shl	shr	string	then
threadvar	to	try	type	until	unit
uses	var	while	with	xor

1.3 Instruction character

Directives are also words with special meanings . Directives are only used in special program locations or meaningful program segments when context is associated , It can be redefined in other occasions .Object Pascal Specified in the 39 Directive characters ：

Instruction character
absolute	abstract	assembler	automated	cdecl	contains
default	dispid	dynamic	export	external	far
forward	implements	index	message	name	near
nodefault	overload	override	package	pascal	private
protected	public	published	read	readonly	register
reintroduce	requires	resident	safecall	stdcall	stored
virtual	write	writeonly

1.4 Summary of reserved words and directives

Reserved word or directive	purpose
absolute	Instructions ( Variable )
abstract	Instructions ( Method )
and	Operator ( Boolean )
array	type
as	Operator (RTTI)
asm	sentence
assembler	Backward compatibility ( assembly )
at	sentence ( exception handling )
automated	Access the category symbol ( class )
begin	Block marker
case	sentence
cdecl	Function call protocol
class	type
const	A statement or instruction ( Parameters )
constructor	Special methods
contains	Operator ( aggregate )
default	Instructions ( attribute )
destructor	Special methods
dispid	dispinterface Interface class symbol
dispinterface	type
div	Operator
do	sentence
downto	sentence (for)
dynamic	Instructions ( Method )
else	sentence (if or case)
end	Block marker
except	sentence ( exception handling )
export	Backward compatibility ( class )
exports	Statement
external	Instructions ( function )
far	Backward compatibility ( class )
file	type
finalization	Unit structure
finally	sentence ( exception handling )
for	sentence
forward	Function instructions
function	Statement
goto	sentence
if	sentence
implementation	Unit structure
implements	Instructions ( attribute )
in	Operator ( aggregate )
index	Instructions (dispinterface Interface )
inherited	sentence
initialization	Unit structure
inline	Backward compatibility ( see asm)
interface	type
is	Operator (RTTI)
label	Statement
library	Program structure
message	Instructions ( Method )
mod	Operator ( mathematics )
name	Instructions ( function )
near	Backward compatibility ( class )
nil	The number
nodefault	Instructions ( attribute )
not	Operator ( Boolean )
object	Backward compatibility ( class )
of	sentence (case)
on	sentence ( exception handling )
or	Operator ( Boolean )
out	Instructions ( Parameters )
overload	Function instructions
override	Function instructions
package	Program structure ( Control pack )
packed	Instructions ( Record )
pascal	Function call protocol
private	Access the category symbol (class)
procedure	Statement
program	Program structure
property	Statement
protected	Access the category symbol ( class )
public	Access the category symbol ( class )
published	Access the category symbol ( class )
raise	sentence ( exception handling )
read	Property class
readonly	dispatch Interface class symbol
record	type
register	Function call protocol
reintroduce	Function instructions
repeat	sentence
requires	Program structure ( Control pack )
resident	Instructions ( function )
resourcestring	type
safecall	Function call protocol
set	type
shl	Operator ( mathematics )
shr	Operator ( mathematics )
stdcall	Function call protocol
stored	Instructions ( attribute )
string	type
then	sentence (if)
threadvar	Statement
to	sentence (for)
try	sentence ( exception handling )
type	Statement
unit	Unit structure
until	sentence
uses	Unit structure
var	Statement
virtual	Instructions ( Method )
while	sentence
with	sentence
write	Property class
writeonly	dispatch Interface class symbol
xor	Operator ( Boolean )

1.5 notes

Object Pascal Notes in language ：

• Combination symbol { And } Use in pairs to indicate that the included content is annotation content .

• Combination symbol (* And *) Use in pairs to indicate that the included content is annotation content .

• Symbol // The single use of indicates that the content after the symbol in the line is the annotation content .

for example ：

{ Curly bracket comment }
(* parentheses / Asterisk notes *)
//C++ Style notes 

Be careful , Do not nest notes of the same type . Although different types of annotations are syntactically legitimate , But this is not recommended . for example ：

{(* It's legal *)}
(*{ It's legal }*)
(*(* It's illegal *)*)
{
  { It's illegal }}