What’s the difference between Float and Double in Swift

Published by donnywals on

A Double and Float are both used to represent decimal numbers, but they do so in slightly different ways.

If you initialize a decimal number in Swift using as shown below, the Swift compiler will assume that you meant to create a Double:

let val = 3.123 // val is inferred to be Double

The reason for this is that Double is the more precise type when comparing it to Float. A Float holds a total of 8 positions, or 32 bits. Since Double is more precise, it can hold more positions. It uses 64 bits to do this. In practice, that means the following:

print(Double.pi) // 3.141592653589793
print(Float.pi) // 3.1415925

As you can see, Double can represent pi far more accurately than Float. We can make the difference more obvious if we multiply pi by 1000:

print(Double.pi * 1000) // 3141.592653589793
print(Float.pi * 1000) // 3141.5925

Both Double and Float sacrifice some after the comma precision when you multiply pi by 1000. For Float this means that it only has four decimal places while Double still has twelve.

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