Hands-On Design Patterns and Best Practices with Julia

Understanding why constants help performance

The compiler has a lot more freedom when dealing with constants because of the following:

• The value does not change.
• The type of the constant does not change. 

This will become clear after we look into some simple examples.

Let's take a look at the following function:

function constant_folding_example()    a = 2 * 3    b = a + 1    return b > 1 ? 10 : 20end

If we just follow the logic, then it is not difficult to see that it always returns a value of 10. Let's just unroll it quickly here:

• The a variable has a value of 6.
• The b variable has a value of a + 1, which is 7.
• Because the b variable is greater than 1, it returns 10.

From the compiler's perspective, the a variable can be inferred as a constant ...