Exception Handling in Dao

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Exception Handling in Dao

Dao exceptions are organized into hierarchal structured classes. The base class is Exception ,

class Exception( content='' )
{
protected
my Rout = '';
my File = '';
my FromLine = 0;
my ToLine = 0;
public
my Name = 'Exception';
my Content : any = 'undefined exception';
if( content ) Content = content;
}

Currently supported classes are the following:

Class	Exception Type
Exception	Any
Exception.None	None
Exception.Any	Any or none
Exception.Error	Any error
Exception.Warning	Any warning
Exception.Error.Field	invalid field accessing
Exception.Error.Field.NotExist	field not exist
Exception.Error.Field.NotPermit	field not permit
Exception.Error.Float	invalid floating point operation
Exception.Error.Float.DivByZero	division by zero
Exception.Error.Float.OverFlow	floating point overflow
Exception.Error.Float.UnderFlow	floating point underflow
Exception.Error.Index	invalid index
Exception.Error.Index.OutOfRange	index out of range
Exception.Error.Key	invalid key
Exception.Error.Key.NotExist	key not exist
Exception.Error.Param	invalid parameter list for the call
Exception.Error.Syntax	invalid syntax
Exception.Error.Type	invalid variable type for the operation
Exception.Error.Value	invalid variable value for the operation

New exception classes can be derived from the above classes.

Any running time error will raise a proper exception instance. User-defined exception can be raised by using raise statement. Exceptions can be rescued by a block of code after a rescue statement The exception handling syntax is the following:

stmt_tryrescue ::=
     'try' '{' stmt_block
     { '}' 'rescue' [ '(' expr ')' ] '{' stmt_block }*
     '}'

where expr is a list of exception class(es). If there is no expr following rescue , any exception will be rescued. There can be multiple rescue statements in a try-rescue block. The raised exceptions will be checked against the exception classes presented in each of the rescue statement, if there is a matching, the corresponding code block is executed, and the rescued exceptions can be accessed in a global list named exceptions . In the same try-rescue block different rescue statements can be used to handle different exceptions.

If all rescue statements have been tried and there is still un-rescued exception(s), the current function is aborted and the exceptions(s) is raised to its caller, if there is; otherwise, the program is aborted with the values of the un-rescued exceptions printed out. In a rescue statement, one may modify exection condition, and use retry to invoke the codes in try block.

Examples,

try{
     raise Exception.Error( "error test" ), Exception.Warning( "warning test" ),
     Exception( "exception" );
}rescue( Exception.Error, Exception.Warning ){
     stdio.println( exceptions );
}rescue{
     stdio.println( "rescued" );
}

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created at 2009-09-18, 06:38 GMT

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Exception Handling in Dao