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I am looking though some source code from a third party and am repeatedly seeing a syntax that is new to me. Basically they are separating statements with commas instead of semicolons. It compiles and works, but I don’t understand what it is doing. It looks like so
if(url)[url release], url = nil;
and they also use it without the if sometimes
[url release], url = nil;
What’s going on here?
As in C and C++, the comma operator computes the thing on its left side and then computes the thing on the right; the overall value of the expression is the value of the right side. Basically, this lets a single expression do two things (the one on the left side being presumably for side effects such as a method call or assignment). Yes, the syntax is somewhat ambiguous with that used in function calls and variable declarations.
I prefer to use an honest block containing multiple statements where possible. Longer, but ultimately cleaner. Easier to debug too.