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From: Aleksandar Fabijanic <aleks.fabijanic@gmail.com>
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Subject: Re: optional<T>, one more value or two states
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On Fri, Jan 25, 2013 at 4:17 PM, Tony V E <tvaneerd@gmail.com> wrote:
>>
>> Is there a difference between empty and null?
>>
> Is there a difference between empty and null?

There is difference, here are some real world examples:

1) see https://github.com/pocoproject/poco/blob/develop/Foundation/include/Poco/Optional.h#L70
:

/// Note that the Optional class is basically the same as
/// Nullable. However, serializers may treat Nullable
/// and Optional differently. An example is XML serialization based
/// on XML Schema, where Optional would be used for an element with
/// minOccurs == 0, whereas Nullable would be used on an element with
/// nillable == true.

2) Another example is how different databases treat empty string,
see https://github.com/pocoproject/poco/blob/develop/Data/include/Poco/Data/AbstractSessionImpl.h#L99
:

/// Adds "emptyStringIsNull" feature and sets it to false. This
feature should be
/// set to true in order to modify the behavior of the databases that
distinguish
/// between zero-length character strings as nulls. Setting this
feature to true
/// shall disregard any difference between empty character strings and nulls,
/// causing the framework to treat them the same (i.e. behave like Oracle).

Alex

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