副作用和参考透明度有什么区别？

Question

What is the difference between these terms?

• a function has no side effect

• a function is referential transparent

Answer 1

A function that is referentially transparent definitely has no side effects. However, a function that has no side effects is not always referentially transparent.

Examples:

int x = 0;

int referentiallyTransparent(int y)
{
    return y + 1;
}

int hasNoSideEffects(int y)
{
    return x + y;
}

The function hasNoSideEffects has no side effects. Which means that calling hasNoSideEffects(y) does not affect the state of the program. However, the value it returns is affected by the state of the program and does not solely depend on the input variable y and thus a call hasNoSideEffects(y) cannot always be replaced by the value it reduces to.