What Does @ Mean?

[XavierAP]

On Monday, 8 April 2019 at 11:58:49 UTC, Ron Tarrant wrote:
>
> And while I'm asking, does an underscore have special meaning 
> when used either at the beginning or end of a variable name?

In D, @ is used as Adam has explained as a prefix indicating 
attributes (either user-defined ones or, confusingly enough, some 
of the standard ones).

The only other example of language using @, in an almost but not 
quite completely different way, is C#. It's also a prefix that 
allows you to define names that would collide with reserved 
words, for example string @class = "menu"; Of course you should 
never do this unless you absolutely need for interop.

Underscore prefixes are used in some languages by pure user 
convention mainly for private members (fields), to avoid name 
clashing. For example in D you could have a public property 
length and a private member _length.

Python takes this a step further. Since it supports classes but 
no public/private visibility at all, users and IDEs have convened 
to use (one or two) underscore prefixes to signal members that 
aren't meant to be accessed publicly from outside the class, even 
if there's nothing stopping you (besides auto code completion not 
showing them).

For C and C++ the convention (recognized by the standards) is 
different: names prefixed by any number of underscores are all 
reserved; basically because the global namespace is so badly 
polluted already. In this case I've seen some other annoying 
conventions, for example private member variables being prefixed 
with m_