What would we do without NULL?

Question

I once read that having nullable types is an absolute evil. I believe it was in an article written by the very person who created them(in Ada?) I believe this is the article

Answer 1

Tcl is one language that not only does not have the concept of null but where the concept of null itself is at odds with the core of the language. In tcl we say: 'everything is a string'. What it really means is tcl has a strict value semantics (which just happens to default to strings).

So what do tcl programmers use to represent "no-data"? Mostly it's the empty string. In some cases where the empty string can represent data then its typically one of:

1. Use empty string anyway - the majority of the time it makes no difference to the end user.

2. Use a value you know won't exist in the data stream - for example the string "_NULL_" or the number 9999999 or my favourite the NUL byte "\0".

3. Use a data structure wrapped around the value - the simplest is a list (what other languages call arrays). A list of one element means the value exist, zero element means null.

4. Test for the existence of the variable - [info exists variable_name].

It is interesting to note that Tcl is not the only language with strict value semantics. C also has strict value semantics but the default semantics of values just happen to be integers rather than strings.

Oh, almost forgot another one:

Some libraries use a variation of number 2 that allows the user to specify what the placeholder for "no data" is. Basically it's allowing you to specify a default value (and if you don't the default value usually defaults to an empty string).