Difference between revisions of "As"
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| + | {{as}} | ||
| − | == | + | The [[Operator|operator]] <syntaxhighlight lang="pascal" inline>as</syntaxhighlight> performs a conditional [[Typecast|typecast]]. |
| + | The word <syntaxhighlight lang="pascal" inline>as</syntaxhighlight> is a [[Reserved word|reserved word]] in [[Mode Delphi|<syntaxhighlight lang="pascal" inline>{$mode Delphi}</syntaxhighlight>]] and [[Mode ObjFPC|<syntaxhighlight lang="pascal" inline>{$mode objFPC}</syntaxhighlight>]]. | ||
| + | == operation == | ||
| + | <syntaxhighlight lang="pascal" inline>as</syntaxhighlight> requires a [[Class|<syntaxhighlight lang="pascal" inline>class</syntaxhighlight>]] or (COM) interface as the first argument and a class or interface reference as the second. | ||
| + | The expression <syntaxhighlight lang="pascal" inline>child as super</syntaxhighlight> is equivalent to the expression and statement: | ||
| + | <syntaxhighlight lang="pascal"> | ||
| + | super(child) | ||
| + | if not assigned(child) and_then not child is super then | ||
| + | begin | ||
| + | raise exception.create(sErrInvalidTypecast); | ||
| + | end; | ||
| + | </syntaxhighlight> | ||
| + | {{Warning|Typecasting a [[Nil|<syntaxhighlight lang="pascal" inline>nil</syntaxhighlight> pointer]] will not raise an exception.}} | ||
| + | However, trying to de-reference <syntaxhighlight lang="pascal" inline>nil</syntaxhighlight> by attempting to access an attribute or method ''will'' cause a [[runtime error|RTE]]. | ||
| − | + | == application == | |
| − | + | <syntaxhighlight lang="pascal" inline>as</syntaxhighlight> ensures a typecast is legit. | |
| − | <syntaxhighlight> | ||
| − | |||
| − | |||
| − | |||
| − | |||
| − | </syntaxhighlight> | ||
| − | + | <syntaxhighlight lang="pascal" inline>as</syntaxhighlight> is one of the operators that can not be [[Operator overloading|overloaded]]. | |
| − | + | == see also == | |
| + | * [[Is|<syntaxhighlight lang="pascal" inline>is</syntaxhighlight>]] | ||
Latest revision as of 17:23, 6 August 2022
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The operator as performs a conditional typecast.
The word as is a reserved word in {$mode Delphi} and {$mode objFPC}.
operation
as requires a class or (COM) interface as the first argument and a class or interface reference as the second.
The expression child as super is equivalent to the expression and statement:
super(child)
if not assigned(child) and_then not child is super then
begin
raise exception.create(sErrInvalidTypecast);
end;
Warning: Typecasting a nil pointer will not raise an exception.
However, trying to de-reference nil by attempting to access an attribute or method will cause a RTE.
application
as ensures a typecast is legit.
as is one of the operators that can not be overloaded.
