There are several different passing modes that govern the relationship between the actual parameter and the formal parameter. The passing mode determines, for example, whether assignments made to the formal parameter are reflected by the actual parameter. The passing mode can also make a large difference in program performance in cases where the actual parameter is an expression. The three types of passing modes available are call-by-value, call-by-name, and call-by-reference.

The following subsections describe the three types of passing modes and explain how you can specify which passing mode is used.