Question

Describe the difference between name equivalence and structure equivalence and describe the difference between their use in modern programming languages. In your answer, clearly define both types of equivalence and show an example in a programming language for each type of equivalence.

Answer 1

There are two standard ways to determine whether two types are considered the same:

1. Name equivalence
2. Structural equivalence.

There can be many differences between the name equivalence and structure equivalence.
Some of them are as follows:

Name equivalence:

• It is the simplest type. Two types are equal if, and only if, they have the same name.
• The meaning of basic operations such as assignment operator (denoted by "=" in C language) is specified in a language definition.
• For example, the meaning of statements such as
  variableA = variableB;
  here the value of object y is copied into the memory locations for variable x.

Structural equivalence:

• By using structural equivalence, two different types are equal only if, they have the same structure which we may implement in different ways.
• For this type of equivalence, the basic requirement is that they have the same component type in the same order.
• Using structural equivalence the two types
  Stack and Set
  would be considered equivalent, which means that a translator would accept statements such as
  stackA = setA

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