1 if there's a return exp; statement 2 if there's a throw statement 4 if there's an assert(0) 8 if there's inline asm 16 if there are multiple return statements
The D Programming Language's Unofficial Docs
beta
1 if there's a return exp; statement 2 if there's a throw statement 4 if there's an assert(0) 8 if there's inline asm 16 if there are multiple return statements