Difference between revisions of "With"

From Free Pascal wiki
Jump to navigationJump to search
(Created page with "{{With}} The reserved word <syntaxhighlight lang="pascal" enclose="none">with</syntaxhighlight> allows a shortened spelling of records. It is on...")
 
(→‎Routing: update source code link)
 
(9 intermediate revisions by 3 users not shown)
Line 1: Line 1:
−
{{With}}
+
{{with}}
  
−
The [[Reserved word|reserved word]] <syntaxhighlight lang="pascal" enclose="none">with</syntaxhighlight> allows a shortened spelling of [[Record|records]]. It is only used in conjunction with the [[Do|<syntaxhighlight lang="pascal" enclose="none">do</syntaxhighlight>]] reserved word.
+
The [[Reserved word|reserved word]] <syntaxhighlight lang="pascal" inline>with</syntaxhighlight> allows overriding the scope lookup routing for named scopes for the duration of one [[statement]].
  
−
Example:
+
== Routing ==
−
<syntaxhighlight>
 
−
// Definition of the record
 
−
type
 
−
  TreRecord = record
 
−
    strValue: string;
 
−
    intValue: integer;
 
−
    dblValue: double;
 
−
  end;
 
  
−
var
+
[[Identifier]]s are searched in the following order, until there is a hit:
−
  reRecord: TreRecord; // Create the record
 
  
−
begin
+
# current [[Block|block]]
−
  ...
+
# enclosing block, if any
 +
# the block enclosing the enclosing block, if any
 +
# … (and so on)
 +
# the most recently imported module, that means for instance the [[Unit|unit]] that appears at the end of the [[Uses|<syntaxhighlight lang="pascal" inline>uses</syntaxhighlight>-clause]] list, if any
 +
# the penultimate module that has been imported, if any
 +
# … (and so on)
 +
# the first imported module, that means for instance the first unit appearing in a <syntaxhighlight lang="pascal" inline>uses</syntaxhighlight>-clause, if any
 +
# additional automatically loaded units, for example, in a [[Program|<syntaxhighlight lang="pascal" inline>program</syntaxhighlight>]] if enabled, the [[heaptrc|<syntaxhighlight lang="pascal" inline>heapTrc</syntaxhighlight> unit]] (see procedure {{gitlab|repository|FPC|release_3_2_0/compiler/pmodules.pas#L318-L412|<syntaxhighlight lang="pascal" inline>loaddefaultunits</syntaxhighlight> in <syntaxhighlight lang="text" inline>compiler/pmodules.pas</syntaxhighlight>}} for a full list)
 +
# the [[System unit|system unit]] (unless implicit inclusion has been disabled)
  
−
  // standard notation:
+
== Override ==
−
  reRecord.strValue := 'Test';
 
−
  reRecord.intValue := 5;
 
−
  reRecord.dblValue := 4.2;
 
  
−
  // When used with
+
The lookup order can be temporarily overridden with a <syntaxhighlight lang="pascal" inline>with</syntaxhighlight>-clause. It looks like this:
−
  with reRecord do
+
 
−
  begin
+
<syntaxhighlight lang="pascal">
−
    strValue := 'Test';
+
with namedScope do
−
    intValue := 5;
+
begin
−
    dblValue := 4.2;
+
…
−
  end;
+
end;
−
  ...
+
</syntaxhighlight>
−
end;
+
 
 +
This puts <syntaxhighlight lang="pascal" inline>namedScope</syntaxhighlight> at the top of the routing.
 +
Identifiers are looked up in <syntaxhighlight lang="pascal" inline>namedScope</syntaxhighlight> first, before other scopes are considered.
 +
 
 +
<syntaxhighlight lang="pascal" inline>namedScope</syntaxhighlight> may be
 +
* the name of a [[Unit|<syntaxhighlight lang="pascal" inline>unit</syntaxhighlight>]] that has previously been imported via a [[Uses|<syntaxhighlight lang="pascal" inline>uses</syntaxhighlight>-clause]] in the current section
 +
* the name of a structured variable, that could have named members, i. e.
 +
** a [[Record|<syntaxhighlight lang="pascal" inline>record</syntaxhighlight>]]
 +
** [[Object|<syntaxhighlight lang="pascal" inline>object</syntaxhighlight>]], or
 +
** [[Class|<syntaxhighlight lang="pascal" inline>class</syntaxhighlight>]].
 +
 
 +
If multiple <syntaxhighlight lang="pascal" inline>with</syntaxhighlight>-clauses ought to be nested, there is the short notation:
 +
<syntaxhighlight lang="pascal">
 +
with snakeOil, sharpTools do
 +
begin
 +
…
 +
end;
 +
</syntaxhighlight>which is equivalent to:<syntaxhighlight lang="pascal">
 +
with snakeOil do
 +
begin
 +
with sharpTools do
 +
begin
 +
…
 +
end;
 +
end;
 
</syntaxhighlight>
 
</syntaxhighlight>
 +
 +
Note, [[Begin|<syntaxhighlight lang="pascal" inline>begin</syntaxhighlight>]]-[[End|<syntaxhighlight lang="pascal" inline>end</syntaxhighlight>]] are not part of the syntax, but <syntaxhighlight lang="pascal" inline>with</syntaxhighlight> … [[Do|<syntaxhighlight lang="pascal" inline>do</syntaxhighlight>]] has to be followed by exactly ''one'' statement.
 +
In practice this will always be a compound statement, though.
 +
 +
== See also ==
 +
 +
* [[Namespaces|namespaces]]

Latest revision as of 01:35, 7 December 2021

│ Deutsch (de) │ English (en) │ suomi (fi) │ русский (ru) │

The reserved word with allows overriding the scope lookup routing for named scopes for the duration of one statement.

Routing

Identifiers are searched in the following order, until there is a hit:

  1. current block
  2. enclosing block, if any
  3. the block enclosing the enclosing block, if any
  4. … (and so on)
  5. the most recently imported module, that means for instance the unit that appears at the end of the uses-clause list, if any
  6. the penultimate module that has been imported, if any
  7. … (and so on)
  8. the first imported module, that means for instance the first unit appearing in a uses-clause, if any
  9. additional automatically loaded units, for example, in a program if enabled, the heapTrc unit (see procedure loaddefaultunits in compiler/pmodules.pas for a full list)
  10. the system unit (unless implicit inclusion has been disabled)

Override

The lookup order can be temporarily overridden with a with-clause. It looks like this: 

	with namedScope do
	begin
		…
	end;

This puts namedScope at the top of the routing. Identifiers are looked up in namedScope first, before other scopes are considered.

namedScope may be

  • the name of a unit that has previously been imported via a uses-clause in the current section
  • the name of a structured variable, that could have named members, i. e.

If multiple with-clauses ought to be nested, there is the short notation: 

	with snakeOil, sharpTools do
	begin
		…
	end;

which is equivalent to:

	with snakeOil do
	begin
		with sharpTools do
		begin
			…
		end;
	end;

Note, begin-end are not part of the syntax, but with … do has to be followed by exactly one statement. In practice this will always be a compound statement, though.

See also

Retrieved from "http://wiki.freepascal.org/index.php?title=With&oldid=148336"