I'm not an expert, but I can bring some of my C experience to bear.

The C language is bound closely to assembler, and as such has certain keywords that act like the attributes that you're talking about. One that comes to mind is volatile, a variable declaration modifier that signals the compiler that whenever that variable was used in an expression, its value had to be read from the memory location assigned to it -- because its value was volatile.

Another example is the lock attribute discussed in the Camel (pp. 457-458); it gives the compiler a hint that only the thread that has locked a function is allowed to call it. This is an attempt to prevent a race condition.

Finally, there's the oxymoron of the constant variable -- that's just a convenience that allows a constant value to be stored in a read-only variable. Any attempt to update this variable's value will be ignored.

So to answer your question -- attributes are used to give hints to the compiler and the run-time about special treatment to be given to certain variables and functions. And sometimes that behaviour isn't fully defined -- it's to leave future perl developers (note the lower case 'p') room to expand, as necessary.

Alex / talexb / Toronto

"Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds

In reply to Re: How Are Attributes Useful? by talexb
in thread How Are Attributes Useful? by Limbic~Region

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