Iterate this dsymbol or members of this scoped dsymbol, then call fp with the found symbol and param.
function pointer to process the iterated symbol. If it returns nonzero, the iteration will be aborted.
a parameter passed to fp.
nonzero if the iteration is aborted by the return value of fp, or 0 if it's completed.
See Implementation
Iterate this dsymbol or members of this scoped dsymbol, then call fp with the found symbol and param.