[pornel]

You can use C99 struct literals:

    return (struct x){a,b};

Small structs may be passed in registers. http://stackoverflow.com/a/3355560/27009

[drpancake]

IIRC passing Obj-C object pointers in C structs is disallowed or discouraged by ARC.

[DrJokepu]

You have to explicitly bridge them in or out of ARC and indicate the ownership rules. Sometimes, for example when you're interfacing straight C code, you have no other option.