From: sto.mar@...
Date: 2013-02-12T18:57:13+09:00
Subject: Re: elegant way to determine if something is defined

Am 11.02.2013 22:28, schrieb Matthew Kerwin:
> sto.mar wrote in post #1096319:
>> Hmmm... very dangerous.
>>
>> That would catch all kinds of exceptions, not only the NameError:
>>
>>     a = []
>>     b = a + 1
>>     # => TypeError: can't convert Fixnum into Array
>>
>> vs.
>>
>>     a = []
>>     b = a + 1 rescue 99
>>     b  # => 99
>
> Back in the olden days, MOO code had the following:
>
>      `x + 1 ! E_TYPE';
> ... returns (x+1) or E_TYPE, or raises E_VARNF.
>
>      `x.y ! E_PROPNF, E_PERM => 17'
> ... returns x.y if x is an object and x.y is a readable property;
> returns 17 if x is an object but x.y is not defined or
> not readable; or raises something else (like E_VARNF or E_INVIND)
>
>      `1 / 0 ! ANY';
> ... returns E_DIV
>
> I liked being able to explicitly trap a certain class of exception, and
> either return the exception itself or a default value.
>
> Additionally it had try/catch blocks.
>
> [1] http://files.moo.ca/1/1/7/ProgrammersManual_26.html#SEC26
>

b = a + 1  rescue $!
b  # => #<NameError: undefined local variable or method `a' for main:Object>


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