Error handling

D includes support for exception-based error handling. Another option is a popular feature called the scope statement.

Scope guards

In a C function that manipulates a locally allocated buffer, it's not unusual to see a series of if…else blocks where, after the failure of some operation, either the buffer is freed directly or via a goto statement. In D, we need neither idiom:

void manipulateData() {
  import core.stdc.stdlib : malloc, free;
  auto buf = cast(ubyte*)malloc(1024);
  scope(exit) if(buf) free(buf);
  // Now do some work with buf
}

Here, memory is allocated outside the GC with malloc and should be released when the function exits. The highlighted scope(exit) allows that. Scope statements are executed at the end of any scope in which they are declared, be it a function body, a loop body, or any block scope. exit says the statement should always be executed when the scope exits. There are two other possible identifiers to use here: success means to execute...