Question

I used to use prefix underscore for instance variable naming, to distinguish from local variables.

I happend to see the “Google Objective-C Style Guide”, and found that it suggests to use trailing underscores(refer it HERE), but without any detail explanation about why.

I know it is a coding style issue, but I do wonder is there any advantages of using trailing underscores?

Answer 1

Related: Question about @synthesize (see the blockquotes at the bottom of the answer)
The advantage is: _var is a convention (C99, Cocoa guidelines) for private, but it is so common (even on Apple templates) that Apple uses double underscore __var. Google solves it by using trailing underscore instead.

I updated the other answer with a couple more reasons…

Leading underscore is also discouraged in C++ (see
What are the rules about using an underscore in a C++ identifier?) and Core Data properties
(try adding a leading underscore in the model and you’ll get “Name
must begin with a letter”).

Trailing underscore seems the sensible choice, but if you like
something else, collisions are unlikely to happen, and if they do,
you’ll get a warning from the compiler.